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typetraits: make genericHead docs reflect reality; use runnableExamples (#16776) [backport:1.4]

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Timothee Cour 2021-01-22 06:06:45 -08:00 • committed by GitHub
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2 changed files with 24 additions and 17 deletions
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34
lib/pure/typetraits.nim
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@ -28,29 +28,32 @@ proc arity*(t: typedesc): int {.magic: "TypeTrait".} =
assert arity(array[3, int]) == 2 assert arity(array[3, int]) == 2
assert arity((int, int, float, string)) == 4 assert arity((int, int, float, string)) == 4
proc genericHead*(t: typedesc): typedesc {.magic: "TypeTrait".} proc genericHead*(t: typedesc): typedesc {.magic: "TypeTrait".} =
## Accepts an instantiated generic type and returns its ## Accepts an instantiated generic type and returns its
## uninstantiated form. ## uninstantiated form.
##
## For example:
## * `seq[int].genericHead` will be just `seq`
## * `seq[int].genericHead[float]` will be `seq[float]`
##
## A compile-time error will be produced if the supplied type ## A compile-time error will be produced if the supplied type
## is not generic. ## is not generic.
## ##
## See also: ## See also:
## * `stripGenericParams <#stripGenericParams,typedesc>`_ ## * `stripGenericParams <#stripGenericParams,typedesc>`_
## runnableExamples:
## Example: type
## Foo[T] = object
## .. code-block:: nim FooInst = Foo[int]
## type Foo2 = genericHead(FooInst)
## Functor[A] = concept f doAssert Foo2 is Foo and Foo is Foo2
## type MatchedGenericType = genericHead(typeof(f)) doAssert genericHead(Foo[seq[string]]) is Foo
## # `f` will be a value of a type such as `Option[T]` doAssert not compiles(genericHead(int))
## # `MatchedGenericType` will become the `Option` type
type Generic = concept f
type _ = genericHead(typeof(f))
proc bar(a: Generic): typeof(a) = a
doAssert bar(Foo[string].default) == Foo[string]()
doAssert not compiles bar(string.default)
when false: # these don't work yet
doAssert genericHead(Foo[int])[float] is Foo[float]
doAssert seq[int].genericHead is seq
proc stripGenericParams*(t: typedesc): typedesc {.magic: "TypeTrait".} proc stripGenericParams*(t: typedesc): typedesc {.magic: "TypeTrait".}
## This trait is similar to `genericHead <#genericHead,typedesc>`_, but ## This trait is similar to `genericHead <#genericHead,typedesc>`_, but
@ -168,7 +171,6 @@ macro genericParamsImpl(T: typedesc): untyped =
ret = newTree(nnkBracketExpr, @[bindSym"range", ai]) ret = newTree(nnkBracketExpr, @[bindSym"range", ai])
else: else:
since (1, 1): since (1, 1):
echo ai.typeKind
ret = newTree(nnkBracketExpr, @[bindSym"StaticParam", ai]) ret = newTree(nnkBracketExpr, @[bindSym"StaticParam", ai])
result.add ret result.add ret
break break

7
tests/metatype/ttypetraits.nim
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@ -282,7 +282,12 @@ block genericHead:
doAssert not compiles(genericHead(Foo)) doAssert not compiles(genericHead(Foo))
type Bar = object type Bar = object
doAssert not compiles(genericHead(Bar)) doAssert not compiles(genericHead(Bar))
# doAssert seq[int].genericHead is seq
when false: # xxx not supported yet
doAssert seq[int].genericHead is seq
when false: # xxx not supported yet, gives: Error: identifier expected
type Hoo[T] = object
doAssert genericHead(Hoo[int])[float] is Hoo[float]
block: # elementType block: # elementType
iterator myiter(n: int): auto = iterator myiter(n: int): auto =