require_relative '../spec_helper' require_relative 'fixtures/block' describe "A block yielded a single" do before :all do def m(a) yield a end end context "Array" do it "assigns the Array to a single argument" do m([1, 2]) { |a| a }.should == [1, 2] end it "receives the identical Array object" do ary = [1, 2] m(ary) { |a| a }.should equal(ary) end it "assigns the Array to a single rest argument" do m([1, 2, 3]) { |*a| a }.should == [[1, 2, 3]] end it "assigns the first element to a single argument with trailing comma" do m([1, 2]) { |a, | a }.should == 1 end it "assigns elements to required arguments" do m([1, 2, 3]) { |a, b| [a, b] }.should == [1, 2] end it "assigns nil to unassigned required arguments" do m([1, 2]) { |a, *b, c, d| [a, b, c, d] }.should == [1, [], 2, nil] end it "assigns elements to optional arguments" do m([1, 2]) { |a=5, b=4, c=3| [a, b, c] }.should == [1, 2, 3] end it "assgins elements to post arguments" do m([1, 2]) { |a=5, b, c, d| [a, b, c, d] }.should == [5, 1, 2, nil] end it "assigns elements to required arguments when a keyword rest argument is present" do m([1, 2]) { |a, **k| [a, k] }.should == [1, {}] end it "assigns elements to mixed argument types" do result = m([1, 2, 3, {x: 9}]) { |a, b=5, *c, d, e: 2, **k| [a, b, c, d, e, k] } result.should == [1, 2, [], 3, 2, {x: 9}] end it "assigns symbol keys from a Hash to keyword arguments" do result = m(["a" => 1, a: 10]) { |a=nil, **b| [a, b] } result.should == [{"a" => 1}, a: 10] end it "assigns symbol keys from a Hash returned by #to_hash to keyword arguments" do obj = mock("coerce block keyword arguments") obj.should_receive(:to_hash).and_return({"a" => 1, b: 2}) result = m([obj]) { |a=nil, **b| [a, b] } result.should == [{"a" => 1}, b: 2] end ruby_version_is "2.2.1" do # SEGV on MRI 2.2.0 it "calls #to_hash on the argument but does not use the result when no keywords are present" do obj = mock("coerce block keyword arguments") obj.should_receive(:to_hash).and_return({"a" => 1, "b" => 2}) result = m([obj]) { |a=nil, **b| [a, b] } result.should == [{"a" => 1, "b" => 2}, {}] end end it "assigns non-symbol keys to non-keyword arguments" do result = m(["a" => 10, b: 2]) { |a=nil, **b| [a, b] } result.should == [{"a" => 10}, {b: 2}] end it "does not treat hashes with string keys as keyword arguments" do result = m(["a" => 10]) { |a = nil, **b| [a, b] } result.should == [{"a" => 10}, {}] end it "calls #to_hash on the last element if keyword arguments are present" do obj = mock("destructure block keyword arguments") obj.should_receive(:to_hash).and_return({x: 9}) result = m([1, 2, 3, obj]) { |a, *b, c, **k| [a, b, c, k] } result.should == [1, [2], 3, {x: 9}] end it "assigns the last element to a non-keyword argument if #to_hash returns nil" do obj = mock("destructure block keyword arguments") obj.should_receive(:to_hash).and_return(nil) result = m([1, 2, 3, obj]) { |a, *b, c, **k| [a, b, c, k] } result.should == [1, [2, 3], obj, {}] end it "calls #to_hash on the last element when there are more arguments than parameters" do x = mock("destructure matching block keyword argument") x.should_receive(:to_hash).and_return({x: 9}) result = m([1, 2, 3, {y: 9}, 4, 5, x]) { |a, b=5, c, **k| [a, b, c, k] } result.should == [1, 2, 3, {x: 9}] end it "raises a TypeError if #to_hash does not return a Hash" do obj = mock("destructure block keyword arguments") obj.should_receive(:to_hash).and_return(1) lambda { m([1, 2, 3, obj]) { |a, *b, c, **k| } }.should raise_error(TypeError) end it "raises the error raised inside #to_hash" do obj = mock("destructure block keyword arguments") error = RuntimeError.new("error while converting to a hash") obj.should_receive(:to_hash).and_raise(error) lambda { m([1, 2, 3, obj]) { |a, *b, c, **k| } }.should raise_error(error) end it "does not call #to_ary on the Array" do ary = [1, 2] ary.should_not_receive(:to_ary) m(ary) { |a, b, c| [a, b, c] }.should == [1, 2, nil] end end context "Object" do it "calls #to_ary on the object when taking multiple arguments" do obj = mock("destructure block arguments") obj.should_receive(:to_ary).and_return([1, 2]) m(obj) { |a, b, c| [a, b, c] }.should == [1, 2, nil] end it "does not call #to_ary when not taking any arguments" do obj = mock("destructure block arguments") obj.should_not_receive(:to_ary) m(obj) { 1 }.should == 1 end it "does not call #to_ary on the object when taking a single argument" do obj = mock("destructure block arguments") obj.should_not_receive(:to_ary) m(obj) { |a| a }.should == obj end it "does not call #to_ary on the object when taking a single rest argument" do obj = mock("destructure block arguments") obj.should_not_receive(:to_ary) m(obj) { |*a| a }.should == [obj] end it "receives the object if #to_ary returns nil" do obj = mock("destructure block arguments") obj.should_receive(:to_ary).and_return(nil) m(obj) { |a, b, c| [a, b, c] }.should == [obj, nil, nil] end it "raises a TypeError if #to_ary does not return an Array" do obj = mock("destructure block arguments") obj.should_receive(:to_ary).and_return(1) lambda { m(obj) { |a, b| } }.should raise_error(TypeError) end end end # TODO: rewrite describe "A block" do before :each do @y = BlockSpecs::Yielder.new end it "captures locals from the surrounding scope" do var = 1 @y.z { var }.should == 1 end it "allows for a leading space before the arguments" do res = @y.s (:a){ 1 } res.should == 1 end it "allows to define a block variable with the same name as the enclosing block" do o = BlockSpecs::OverwriteBlockVariable.new o.z { 1 }.should == 1 end it "does not capture a local when an argument has the same name" do var = 1 @y.s(2) { |var| var }.should == 2 var.should == 1 end it "does not capture a local when the block argument has the same name" do var = 1 proc { |&var| var.call(2) }.call { |x| x }.should == 2 var.should == 1 end describe "taking zero arguments" do it "does not raise an exception when no values are yielded" do @y.z { 1 }.should == 1 end it "does not raise an exception when values are yielded" do @y.s(0) { 1 }.should == 1 end end describe "taking || arguments" do it "does not raise an exception when no values are yielded" do @y.z { || 1 }.should == 1 end it "does not raise an exception when values are yielded" do @y.s(0) { || 1 }.should == 1 end end describe "taking |a| arguments" do it "assigns nil to the argument when no values are yielded" do @y.z { |a| a }.should be_nil end it "assigns the value yielded to the argument" do @y.s(1) { |a| a }.should == 1 end it "does not call #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_not_receive(:to_ary) @y.s(obj) { |a| a }.should equal(obj) end it "assigns the first value yielded to the argument" do @y.m(1, 2) { |a| a }.should == 1 end it "does not destructure a single Array value" do @y.s([1, 2]) { |a| a }.should == [1, 2] end end describe "taking |a, b| arguments" do it "assgins nil to the arguments when no values are yielded" do @y.z { |a, b| [a, b] }.should == [nil, nil] end it "assigns one value yielded to the first argument" do @y.s(1) { |a, b| [a, b] }.should == [1, nil] end it "assigns the first two values yielded to the arguments" do @y.m(1, 2, 3) { |a, b| [a, b] }.should == [1, 2] end it "does not destructure an Array value as one of several values yielded" do @y.m([1, 2], 3, 4) { |a, b| [a, b] }.should == [[1, 2], 3] end it "assigns 'nil' and 'nil' to the arguments when a single, empty Array is yielded" do @y.s([]) { |a, b| [a, b] }.should == [nil, nil] end it "assigns the element of a single element Array to the first argument" do @y.s([1]) { |a, b| [a, b] }.should == [1, nil] @y.s([nil]) { |a, b| [a, b] }.should == [nil, nil] @y.s([[]]) { |a, b| [a, b] }.should == [[], nil] end it "destructures a single Array value yielded" do @y.s([1, 2, 3]) { |a, b| [a, b] }.should == [1, 2] end it "destructures a splatted Array" do @y.r([[]]) { |a, b| [a, b] }.should == [nil, nil] @y.r([[1]]) { |a, b| [a, b] }.should == [1, nil] end it "calls #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_receive(:to_ary).and_return([1, 2]) @y.s(obj) { |a, b| [a, b] }.should == [1, 2] end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |a, b| [a, b] }.should == [1, 2] end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |a, b| [a, b] }.should == [obj, nil] end it "raises a TypeError if #to_ary does not return an Array" do obj = mock("block yield to_ary invalid") obj.should_receive(:to_ary).and_return(1) lambda { @y.s(obj) { |a, b| } }.should raise_error(TypeError) end it "raises the original exception if #to_ary raises an exception" do obj = mock("block yield to_ary raising an exception") obj.should_receive(:to_ary).and_raise(ZeroDivisionError) lambda { @y.s(obj) { |a, b| } }.should raise_error(ZeroDivisionError) end end describe "taking |a, *b| arguments" do it "assigns 'nil' and '[]' to the arguments when no values are yielded" do @y.z { |a, *b| [a, b] }.should == [nil, []] end it "assigns all yielded values after the first to the rest argument" do @y.m(1, 2, 3) { |a, *b| [a, b] }.should == [1, [2, 3]] end it "assigns 'nil' and '[]' to the arguments when a single, empty Array is yielded" do @y.s([]) { |a, *b| [a, b] }.should == [nil, []] end it "assigns the element of a single element Array to the first argument" do @y.s([1]) { |a, *b| [a, b] }.should == [1, []] @y.s([nil]) { |a, *b| [a, b] }.should == [nil, []] @y.s([[]]) { |a, *b| [a, b] }.should == [[], []] end it "destructures a splatted Array" do @y.r([[]]) { |a, *b| [a, b] }.should == [nil, []] @y.r([[1]]) { |a, *b| [a, b] }.should == [1, []] end it "destructures a single Array value assigning the remaining values to the rest argument" do @y.s([1, 2, 3]) { |a, *b| [a, b] }.should == [1, [2, 3]] end it "calls #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_receive(:to_ary).and_return([1, 2]) @y.s(obj) { |a, *b| [a, b] }.should == [1, [2]] end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |a, *b| [a, b] }.should == [1, [2]] end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |a, *b| [a, b] }.should == [obj, []] end it "raises a TypeError if #to_ary does not return an Array" do obj = mock("block yield to_ary invalid") obj.should_receive(:to_ary).and_return(1) lambda { @y.s(obj) { |a, *b| } }.should raise_error(TypeError) end end describe "taking |*| arguments" do it "does not raise an exception when no values are yielded" do @y.z { |*| 1 }.should == 1 end it "does not raise an exception when values are yielded" do @y.s(0) { |*| 1 }.should == 1 end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |*| 1 }.should == 1 end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |*| 1 }.should == 1 end it "does not call #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_not_receive(:to_ary) @y.s(obj) { |*| 1 }.should == 1 end end describe "taking |*a| arguments" do it "assigns '[]' to the argument when no values are yielded" do @y.z { |*a| a }.should == [] end it "assigns a single value yielded to the argument as an Array" do @y.s(1) { |*a| a }.should == [1] end it "assigns all the values passed to the argument as an Array" do @y.m(1, 2, 3) { |*a| a }.should == [1, 2, 3] end it "assigns '[[]]' to the argument when passed an empty Array" do @y.s([]) { |*a| a }.should == [[]] end it "assigns a single Array value passed to the argument by wrapping it in an Array" do @y.s([1, 2, 3]) { |*a| a }.should == [[1, 2, 3]] end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |*a| a }.should == [[1, 2]] end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |*a| a }.should == [obj] end it "does not call #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_not_receive(:to_ary) @y.s(obj) { |*a| a }.should == [obj] end end describe "taking |a, | arguments" do it "assigns nil to the argument when no values are yielded" do @y.z { |a, | a }.should be_nil end it "assgins the argument a single value yielded" do @y.s(1) { |a, | a }.should == 1 end it "assigns the argument the first value yielded" do @y.m(1, 2) { |a, | a }.should == 1 end it "assigns the argument the first of several values yielded when it is an Array" do @y.m([1, 2], 3) { |a, | a }.should == [1, 2] end it "assigns nil to the argument when passed an empty Array" do @y.s([]) { |a, | a }.should be_nil end it "assigns the argument the first element of the Array when passed a single Array" do @y.s([1, 2]) { |a, | a }.should == 1 end it "calls #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_receive(:to_ary).and_return([1, 2]) @y.s(obj) { |a, | a }.should == 1 end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |a, | a }.should == 1 end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |a, | a }.should == obj end it "raises a TypeError if #to_ary does not return an Array" do obj = mock("block yield to_ary invalid") obj.should_receive(:to_ary).and_return(1) lambda { @y.s(obj) { |a, | } }.should raise_error(TypeError) end end describe "taking |(a, b)| arguments" do it "assigns nil to the arguments when yielded no values" do @y.z { |(a, b)| [a, b] }.should == [nil, nil] end it "destructures a single Array value yielded" do @y.s([1, 2]) { |(a, b)| [a, b] }.should == [1, 2] end it "destructures a single Array value yielded when shadowing an outer variable" do a = 9 @y.s([1, 2]) { |(a, b)| [a, b] }.should == [1, 2] end it "calls #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_receive(:to_ary).and_return([1, 2]) @y.s(obj) { |(a, b)| [a, b] }.should == [1, 2] end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |(a, b)| [a, b] }.should == [1, 2] end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |(a, b)| [a, b] }.should == [obj, nil] end it "raises a TypeError if #to_ary does not return an Array" do obj = mock("block yield to_ary invalid") obj.should_receive(:to_ary).and_return(1) lambda { @y.s(obj) { |(a, b)| } }.should raise_error(TypeError) end end describe "taking |(a, b), c| arguments" do it "assigns nil to the arguments when yielded no values" do @y.z { |(a, b), c| [a, b, c] }.should == [nil, nil, nil] end it "destructures a single one-level Array value yielded" do @y.s([1, 2]) { |(a, b), c| [a, b, c] }.should == [1, nil, 2] end it "destructures a single multi-level Array value yielded" do @y.s([[1, 2, 3], 4]) { |(a, b), c| [a, b, c] }.should == [1, 2, 4] end it "calls #to_ary to convert a single yielded object to an Array" do obj = mock("block yield to_ary") obj.should_receive(:to_ary).and_return([1, 2]) @y.s(obj) { |(a, b), c| [a, b, c] }.should == [1, nil, 2] end it "does not call #to_ary if the single yielded object is an Array" do obj = [1, 2] obj.should_not_receive(:to_ary) @y.s(obj) { |(a, b), c| [a, b, c] }.should == [1, nil, 2] end it "does not call #to_ary if the object does not respond to #to_ary" do obj = mock("block yield no to_ary") @y.s(obj) { |(a, b), c| [a, b, c] }.should == [obj, nil, nil] end it "raises a TypeError if #to_ary does not return an Array" do obj = mock("block yield to_ary invalid") obj.should_receive(:to_ary).and_return(1) lambda { @y.s(obj) { |(a, b), c| } }.should raise_error(TypeError) end end describe "taking nested |a, (b, (c, d))|" do it "assigns nil to the arguments when yielded no values" do @y.m { |a, (b, (c, d))| [a, b, c, d] }.should == [nil, nil, nil, nil] end it "destructures separate yielded values" do @y.m(1, 2) { |a, (b, (c, d))| [a, b, c, d] }.should == [1, 2, nil, nil] end it "destructures a nested Array value yielded" do @y.m(1, [2, 3]) { |a, (b, (c, d))| [a, b, c, d] }.should == [1, 2, 3, nil] end it "destructures a single multi-level Array value yielded" do @y.m(1, [2, [3, 4]]) { |a, (b, (c, d))| [a, b, c, d] }.should == [1, 2, 3, 4] end end describe "taking nested |a, ((b, c), d)|" do it "assigns nil to the arguments when yielded no values" do @y.m { |a, ((b, c), d)| [a, b, c, d] }.should == [nil, nil, nil, nil] end it "destructures separate yielded values" do @y.m(1, 2) { |a, ((b, c), d)| [a, b, c, d] }.should == [1, 2, nil, nil] end it "destructures a nested value yielded" do @y.m(1, [2, 3]) { |a, ((b, c), d)| [a, b, c, d] }.should == [1, 2, nil, 3] end it "destructures a single multi-level Array value yielded" do @y.m(1, [[2, 3], 4]) { |a, ((b, c), d)| [a, b, c, d] }.should == [1, 2, 3, 4] end end describe "arguments with _" do it "extracts arguments with _" do @y.m([[1, 2, 3], 4]) { |(_, a, _), _| a }.should == 2 @y.m([1, [2, 3, 4]]) { |_, (_, a, _)| a }.should == 3 end it "assigns the first variable named" do @y.m(1, 2) { |_, _| _ }.should == 1 end end describe "taking identically-named arguments" do it "raises a SyntaxError for standard arguments" do lambda { eval "lambda { |x,x| }" }.should raise_error(SyntaxError) lambda { eval "->(x,x) {}" }.should raise_error(SyntaxError) lambda { eval "Proc.new { |x,x| }" }.should raise_error(SyntaxError) end it "accepts unnamed arguments" do eval("lambda { |_,_| }").should be_an_instance_of(Proc) eval("->(_,_) {}").should be_an_instance_of(Proc) eval("Proc.new { |_,_| }").should be_an_instance_of(Proc) end end end describe "Block-local variables" do it "are introduced with a semi-colon in the parameter list" do [1].map {|one; bl| bl }.should == [nil] end it "can be specified in a comma-separated list after the semi-colon" do [1].map {|one; bl, bl2| [bl, bl2] }.should == [[nil, nil]] end it "can not have the same name as one of the standard parameters" do lambda { eval "[1].each {|foo; foo| }" }.should raise_error(SyntaxError) lambda { eval "[1].each {|foo, bar; glark, bar| }" }.should raise_error(SyntaxError) end it "can not be prefixed with an asterisk" do lambda { eval "[1].each {|foo; *bar| }" }.should raise_error(SyntaxError) lambda do eval "[1].each {|foo, bar; glark, *fnord| }" end.should raise_error(SyntaxError) end it "can not be prefixed with an ampersand" do lambda { eval "[1].each {|foo; &bar| }" }.should raise_error(SyntaxError) lambda do eval "[1].each {|foo, bar; glark, &fnord| }" end.should raise_error(SyntaxError) end it "can not be assigned default values" do lambda { eval "[1].each {|foo; bar=1| }" }.should raise_error(SyntaxError) lambda do eval "[1].each {|foo, bar; glark, fnord=:fnord| }" end.should raise_error(SyntaxError) end it "need not be preceded by standard parameters" do [1].map {|; foo| foo }.should == [nil] [1].map {|; glark, bar| [glark, bar] }.should == [[nil, nil]] end it "only allow a single semi-colon in the parameter list" do lambda { eval "[1].each {|foo; bar; glark| }" }.should raise_error(SyntaxError) lambda { eval "[1].each {|; bar; glark| }" }.should raise_error(SyntaxError) end it "override shadowed variables from the outer scope" do out = :out [1].each {|; out| out = :in } out.should == :out a = :a b = :b c = :c d = :d {ant: :bee}.each_pair do |a, b; c, d| a = :A b = :B c = :C d = :D end a.should == :a b.should == :b c.should == :c d.should == :d end it "are not automatically instantiated in the outer scope" do defined?(glark).should be_nil [1].each {|;glark| 1} defined?(glark).should be_nil end it "are automatically instantiated in the block" do [1].each do |;glark| glark.should be_nil end end it "are visible in deeper scopes before initialization" do [1].each {|;glark| [1].each { defined?(glark).should_not be_nil glark = 1 } glark.should == 1 } end end describe "Post-args" do it "appear after a splat" do proc do |*a, b| [a, b] end.call(1, 2, 3).should == [[1, 2], 3] proc do |*a, b, c| [a, b, c] end.call(1, 2, 3).should == [[1], 2, 3] proc do |*a, b, c, d| [a, b, c, d] end.call(1, 2, 3).should == [[], 1, 2, 3] end it "are required" do lambda { lambda do |*a, b| [a, b] end.call }.should raise_error(ArgumentError) end describe "with required args" do it "gathers remaining args in the splat" do proc do |a, *b, c| [a, b, c] end.call(1, 2, 3).should == [1, [2], 3] end it "has an empty splat when there are no remaining args" do proc do |a, b, *c, d| [a, b, c, d] end.call(1, 2, 3).should == [1, 2, [], 3] proc do |a, *b, c, d| [a, b, c, d] end.call(1, 2, 3).should == [1, [], 2, 3] end end describe "with optional args" do it "gathers remaining args in the splat" do proc do |a=5, *b, c| [a, b, c] end.call(1, 2, 3).should == [1, [2], 3] end it "overrides the optional arg before gathering in the splat" do proc do |a=5, *b, c| [a, b, c] end.call(2, 3).should == [2, [], 3] proc do |a=5, b=6, *c, d| [a, b, c, d] end.call(1, 2, 3).should == [1, 2, [], 3] proc do |a=5, *b, c, d| [a, b, c, d] end.call(1, 2, 3).should == [1, [], 2, 3] end it "uses the required arg before the optional and the splat" do proc do |a=5, *b, c| [a, b, c] end.call(3).should == [5, [], 3] proc do |a=5, b=6, *c, d| [a, b, c, d] end.call(3).should == [5, 6, [], 3] proc do |a=5, *b, c, d| [a, b, c, d] end.call(2, 3).should == [5, [], 2, 3] end it "overrides the optional args from left to right before gathering the splat" do proc do |a=5, b=6, *c, d| [a, b, c, d] end.call(2, 3).should == [2, 6, [], 3] end describe "with a circular argument reference" do it "shadows an existing local with the same name as the argument" do a = 1 -> { @proc = eval "proc { |a=a| a }" }.should complain(/circular argument reference/) @proc.call.should == nil end it "shadows an existing method with the same name as the argument" do def a; 1; end -> { @proc = eval "proc { |a=a| a }" }.should complain(/circular argument reference/) @proc.call.should == nil end it "calls an existing method with the same name as the argument if explicitly using ()" do def a; 1; end proc { |a=a()| a }.call.should == 1 end end end describe "with pattern matching" do it "extracts matched blocks with post arguments" do proc do |(a, *b, c), d, e| [a, b, c, d, e] end.call([1, 2, 3, 4], 5, 6).should == [1, [2, 3], 4, 5, 6] end it "allows empty splats" do proc do |a, (*), b| [a, b] end.call([1, 2, 3]).should == [1, 3] end end end