This module defines compile-time reflection procs for working with types.
Unstable API.
Example:
import std/typetraits type A = enum a0 = 2, a1 = 4, a2 type B = enum b0 = 2, b1, b2 assert A is enum assert A is HoleyEnum assert A isnot OrdinalEnum assert B isnot HoleyEnum assert B is OrdinalEnum assert int isnot HoleyEnum type C[T] = enum h0 = 2, h1 = 4 assert C[float] is HoleyEnum
Types
OrdinalEnum = Ordinal and enum
- Enum without holes. Source Edit
StaticParam[value] = object
- Used to wrap a static value in genericParams. Source Edit
Procs
proc arity(t: typedesc): int {.magic: "TypeTrait", ...raises: [], tags: [].}
-
Returns the arity of the given type. This is the number of "type" components or the number of generic parameters a given type t has.
Example:
doAssert arity(int) == 0 doAssert arity(seq[string]) == 1 doAssert arity(array[3, int]) == 2 doAssert arity((int, int, float, string)) == 4
Source Edit proc distinctBase(T: typedesc; recursive: static bool = true): typedesc {. magic: "TypeTrait", ...raises: [], tags: [].}
-
Returns the base type for distinct types, or the type itself otherwise. If recursive is false, only the immediate distinct base will be returned.
See also:
Example:
type MyInt = distinct int type MyOtherInt = distinct MyInt doAssert distinctBase(MyInt) is int doAssert distinctBase(MyOtherInt) is int doAssert distinctBase(MyOtherInt, false) is MyInt doAssert distinctBase(int) is int
Source Edit proc genericHead(t: typedesc): typedesc {.magic: "TypeTrait", ...raises: [], tags: [].}
-
Accepts an instantiated generic type and returns its uninstantiated form. A compile-time error will be produced if the supplied type is not generic.
See also:
Example:
type Foo[T] = object FooInst = Foo[int] Foo2 = genericHead(FooInst) doAssert Foo2 is Foo and Foo is Foo2 doAssert genericHead(Foo[seq[string]]) is Foo doAssert not compiles(genericHead(int)) 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
Source Edit proc hasClosure(fn: NimNode): bool {....raises: [], tags: [].}
- Return true if the func/proc/etc fn has closure. fn has to be a resolved symbol of kind nnkSym. This implies that the macro that calls this proc should accept typed arguments and not untyped arguments. Source Edit
proc isNamedTuple(T: typedesc): bool {.magic: "TypeTrait", ...raises: [], tags: [].}
-
Returns true for named tuples, false for any other type.
Example:
doAssert not isNamedTuple(int) doAssert not isNamedTuple((string, int)) doAssert isNamedTuple(tuple[name: string, age: int])
Source Edit proc name(t: typedesc): string {.magic: "TypeTrait", ...raises: [], tags: [].}
-
Returns the name of the given type.
Alias for system.`$`(t) since Nim v0.20.
Example:
doAssert name(int) == "int" doAssert name(seq[string]) == "seq[string]"
Source Edit proc stripGenericParams(t: typedesc): typedesc {.magic: "TypeTrait", ...raises: [], tags: [].}
-
This trait is similar to genericHead, but instead of producing an error for non-generic types, it will just return them unmodified.
Example:
type Foo[T] = object doAssert stripGenericParams(Foo[string]) is Foo doAssert stripGenericParams(int) is int
Source Edit proc supportsCopyMem(t: typedesc): bool {.magic: "TypeTrait", ...raises: [], tags: [].}
-
This trait returns true if the type t is safe to use for copyMem.
Other languages name a type like these blob.
Source Edit
Templates
template distinctBase[T](a: T; recursive: static bool = true): untyped
-
Overload of distinctBase for values.
Example:
type MyInt = distinct int type MyOtherInt = distinct MyInt doAssert 12.MyInt.distinctBase == 12 doAssert 12.MyOtherInt.distinctBase == 12 doAssert 12.MyOtherInt.distinctBase(false) is MyInt doAssert 12.distinctBase == 12
Source Edit template elementType(a: untyped): typedesc
-
Returns the element type of a, which can be any iterable (over which you can iterate).
Example:
iterator myiter(n: int): auto = for i in 0 ..< n: yield i doAssert elementType(@[1,2]) is int doAssert elementType("asdf") is char doAssert elementType(myiter(3)) is int
Source Edit template genericParams(T: typedesc): untyped
-
Returns the tuple of generic parameters for the generic type T.
Note: For the builtin array type, the index generic parameter will always become a range type after it's bound to a variable.
Example:
type Foo[T1, T2] = object doAssert genericParams(Foo[float, string]) is (float, string) type Bar[N: static float, T] = object doAssert genericParams(Bar[1.0, string]) is (StaticParam[1.0], string) doAssert genericParams(Bar[1.0, string]).get(0).value == 1.0 doAssert genericParams(seq[Bar[2.0, string]]).get(0) is Bar[2.0, string] var s: seq[Bar[3.0, string]] doAssert genericParams(typeof(s)) is (Bar[3.0, string],) doAssert genericParams(array[10, int]) is (StaticParam[10], int) var a: array[10, int] doAssert genericParams(typeof(a)) is (range[0..9], int)
Source Edit template get(T: typedesc[tuple]; i: static int): untyped
-
Returns the i-th element of T.
Example:
doAssert get((int, int, float, string), 2) is float
Source Edit template pointerBase[T](_: typedesc[ptr T | ref T]): typedesc
-
Returns T for ref T | ptr T.
Example:
assert (ref int).pointerBase is int type A = ptr seq[float] assert A.pointerBase is seq[float] assert (ref A).pointerBase is A # not seq[float] assert (var s = "abc"; s[0].addr).typeof.pointerBase is char
Source Edit