Merge pull request #8819 from atilaneves/isInputRange-element

Add optional element type to isInputRange

Author: jmdavis

changelog/is_input_range_element.dd

@@ -0,0 +1,7 @@
+isInputRange now takes an optional element type.
+
+isInputRange 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, `isInputRange!(int[], const(int))` is true, but
+`isInputRange!(int[], string)` is false.

std/range/primitives.d

@@ -165,17 +165,21 @@ See_Also:
 
 Params:
     R = type to be tested
+    E = the type of the elements of the range if not `void`
 
 Returns:
-    `true` if R is an input range, `false` if not
+    `true` if R is an input range (possibly with element type `E`), `false` if not
  */
-enum bool isInputRange(R) =
+enum bool isInputRange(R, E = void) =
     is(typeof(R.init) == R)
     && is(typeof((R r) { return r.empty; } (R.init)) == bool)
     && (is(typeof((return ref R r) => r.front)) || is(typeof(ref (return ref R r) => r.front)))
     && !is(typeof((R r) { return r.front; } (R.init)) == void)
-    && is(typeof((R r) => r.popFront));
-
+    && is(typeof((R r) => r.popFront))
+    && (is(E == void) ||
+        is(ElementType!R == E) ||
+        is(const(ElementType!R) == E) ||
+        (is(const(ElementType!R) == immutable E) && is(const(E) == E)));
 ///
 @safe unittest
 {
@@ -192,6 +196,18 @@ enum bool isInputRange(R) =
     static assert( isInputRange!(char[]));
     static assert(!isInputRange!(char[4]));
     static assert( isInputRange!(inout(int)[]));
+    static assert(!isInputRange!(int[], string));
+    static assert( isInputRange!(int[], int));
+    static assert( isInputRange!(int[], const int));
+    static assert(!isInputRange!(int[], immutable int));
+
+    static assert(!isInputRange!(const(int)[], int));
+    static assert( isInputRange!(const(int)[], const int));
+    static assert(!isInputRange!(const(int)[], immutable int));
+
+    static assert(!isInputRange!(immutable(int)[], int));
+    static assert( isInputRange!(immutable(int)[], const int));
+    static assert( isInputRange!(immutable(int)[], immutable int));
 
     static struct NotDefaultConstructible
     {