| | 1 | = Anonymous Methods/Closures and lambdas = |
| | 2 | |
| | 3 | Cobra supports both anonymous methods (also known as closures where they capture the values of surrounding variables if referenced) [[br]] |
| | 4 | and a simpler single line expression form known as lambdas. |
| | 5 | |
| | 6 | Both are introduced with the "'''do'''" keyword. |
| | 7 | |
| | 8 | The syntax for closures is similar to that of the [wiki:Methods def] statement (defining a classes methods) |
| | 9 | except that there is no method name. |
| | 10 | |
| | 11 | The body of the closure follows the line the '''do''' (plus any paramList) is on, indented one level |
| | 12 | |
| | 13 | A lambda uses the same "do" keyword as closures, but the argument list is followed by "=<expr>" all on a single line. |
| | 14 | |
| | 15 | |
| | 16 | == Grammar == |
| | 17 | Anonymous Method |
| | 18 | {{{ |
| | 19 | do [as <Type>] # no parameters |
| | 20 | <body statements...> |
| | 21 | |
| | 22 | do(<paramList>) [as <Type>] |
| | 23 | <body statements...> |
| | 24 | |
| | 25 | For these a parameter list is a comma separated list of name (and optionally type) specifications |
| | 26 | <paramName> [as <Type>] [, ...] |
| | 27 | }}} |
| | 28 | |
| | 29 | |
| | 30 | Lambdas |
| | 31 | {{{ |
| | 32 | do = <expr> # no parameters |
| | 33 | do (<paramList>) = <expr> # args passed as per invocation |
| | 34 | }}} |
| | 35 | |
| | 36 | |
| | 37 | == Examples == |
| | 38 | Anonymous Method |
| | 39 | {{{ |
| | 40 | sig ArithmeticOp(a as int, b as int) as int |
| | 41 | sig SimpleMethod |
| | 42 | # ... |
| | 43 | class Test |
| | 44 | def callArithmeticOp(a as int, b as int, op as ArithmeticOp) as int |
| | 45 | return op(a, b) |
| | 46 | |
| | 47 | def invoke(method as SimpleMethod) |
| | 48 | method() |
| | 49 | |
| | 50 | #... |
| | 51 | def run |
| | 52 | assert 12 == .callArithmeticOp(3, 4, do(a as int, b as int)) |
| | 53 | return a * b |
| | 54 | |
| | 55 | # multiple statements in the anonymous method |
| | 56 | assert 12 == .callArithmeticOp(3, 4, do(a as int, b as int)) |
| | 57 | r = 0 |
| | 58 | for i in a |
| | 59 | r += b |
| | 60 | assert r == a * b |
| | 61 | return r |
| | 62 | |
| | 63 | # access members |
| | 64 | assert 24 == .callArithmeticOp(3, 4, do(a as int, b as int)) |
| | 65 | return a * b * .two |
| | 66 | |
| | 67 | # access local vars |
| | 68 | multiplier = 10 |
| | 69 | assert 120 == .callArithmeticOp(3, 4, do(a as int, b as int)) |
| | 70 | return a * b * multiplier |
| | 71 | |
| | 72 | count = 0 |
| | 73 | .invoke(do) # no parameters |
| | 74 | count += 1 |
| | 75 | assert count == 1 |
| | 76 | }}} |
| | 77 | |
| | 78 | Lambda |
| | 79 | {{{ |
| | 80 | t = [3, 2, 1] |
| | 81 | t.sort(do(a as int, b as int)=a.compareTo(b)) |
| | 82 | }}} |
| | 83 | |
| | 84 | == Notes == |
| | 85 | |
| | 86 | The argument types are not yet inferred which is why you should specify them explicitly typed |
| | 87 | as in the examples above. |
| | 88 | |
| | 89 | Multiple closures on a single line are not yet supported. |
| | 90 | |
| | 91 | You can store a reference to a closure so long as you have a type for its signature. |
| | 92 | e.g |
| | 93 | {{{ |
| | 94 | class Test |
| | 95 | |
| | 96 | def main is shared |
| | 97 | t = [3, 2, 1] |
| | 98 | |
| | 99 | # embedded closure |
| | 100 | t.sort(do(a as int, b as int)) |
| | 101 | return a.compareTo(b) |
| | 102 | |
| | 103 | # store closure in local var |
| | 104 | c as Comparison<of int> = do(a as int, b as int) |
| | 105 | return a.compareTo(b) |
| | 106 | t.sort(c) |
| | 107 | }}} |
