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[std/traits] Improve docs for isCallable #10815

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Merged
merged 4 commits into from
Jul 7, 2025
Merged

[std/traits] Improve docs for isCallable #10815

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9ea534f
[std/traits] Improve docs for `isCallable`
ntrel Jul 7, 2025
ef1bf19
Remove template lambda
ntrel Jul 7, 2025
86a562f
Untyped function literal isn't detected
ntrel Jul 7, 2025
ba11ccf
Expand IFTI
ntrel Jul 7, 2025
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21 changes: 18 additions & 3 deletions std/traits.d
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Original file line number Diff line number Diff line change
Expand Up @@ -7611,6 +7611,8 @@ enum bool isSomeFunction(alias T) =
/**
Detect whether `T` is a callable object, which can be called with the
function call operator `$(LPAREN)...$(RPAREN)`.

$(NOTE IFTI is *not* attempted - see below.)
*/
template isCallable(alias callable)
{
Expand All @@ -7634,7 +7636,7 @@ template isCallable(alias callable)
}
}

/// Functions, lambdas, and aggregate types with (static) opCall.
/// Functions, function pointers, delegates, lambdas.
@safe unittest
{
void f() { }
Expand All @@ -7643,6 +7645,17 @@ template isCallable(alias callable)
static assert( isCallable!f);
static assert( isCallable!g);

auto fp = &f;
static assert( isCallable!fp);
static assert( isCallable!((int x) {}));

int x;
static assert(!isCallable!x);
}

/// Aggregate types with (static) opCall.
@safe unittest
{
class C { int opCall(int) { return 0; } }
auto c = new C;
struct S { static int opCall(int) { return 0; } }
Expand All @@ -7657,7 +7670,7 @@ template isCallable(alias callable)
static assert(!isCallable!I);
}

/// Templates
/// Template functions are only detected if they are instantiable with `!()`.
@safe unittest
{
void f()() { }
Expand All @@ -7669,9 +7682,11 @@ template isCallable(alias callable)
static assert( isCallable!g);
static assert( isCallable!S1);
static assert( isCallable!S2);

static assert(!isCallable!((x) {}));
}

/// Overloaded functions and function templates.
/// Overloaded functions and function templates instantiable with `!()`.
@safe unittest
{
static struct Wrapper
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