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Add optional element type to isForwardRange #8842

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Nov 7, 2023
Merged

Add optional element type to isForwardRange #8842

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7 changes: 7 additions & 0 deletions changelog/is_forward_range_element.dd
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
isForwardRange now takes an optional element type.

isForwardRange now has an optional 2nd template parameter that defaults
to void. If not void, it only evaluates to true if the range's element
type is the same type as this extra argument, modulo const. For
instance, `isForwardRange!(int[], const(int))` is true, but
`isForwardRange!(int[], string)` is false.
15 changes: 15 additions & 0 deletions std/range/primitives.d
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Original file line number Diff line number Diff line change
Expand Up @@ -1015,12 +1015,27 @@ See_Also:
enum bool isForwardRange(R) = isInputRange!R
&& is(typeof((R r) { return r.save; } (R.init)) == R);

/// ditto
enum bool isForwardRange(R, E) =
.isForwardRange!R && isQualifierConvertible!(ElementType!R, E);

///
@safe unittest
{
static assert(!isForwardRange!(int));
static assert( isForwardRange!(int[]));
static assert( isForwardRange!(inout(int)[]));

static assert( isForwardRange!(int[], const int));
static assert(!isForwardRange!(int[], immutable int));

static assert(!isForwardRange!(const(int)[], int));
static assert( isForwardRange!(const(int)[], const int));
static assert(!isForwardRange!(const(int)[], immutable int));

static assert(!isForwardRange!(immutable(int)[], int));
static assert( isForwardRange!(immutable(int)[], const int));
static assert( isForwardRange!(immutable(int)[], immutable int));
}

@safe unittest
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