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On 6/25/22 7:44 PM, WebFreak001 wrote:
>let's see this code:
import std.range;
int[] arr;
arr.put(2);
someone not coming from a D backround (or even those coming from it) might expect here to have arr be equal to [2] afterwards.
However this is not the case:
core.exception.AssertError@/dlang/dmd/linux/bin64/../../src/phobos/std/range/primitives.d(2472): Attempting to fetch the front of an empty array of int
----------------
??:? _d_assert_msg [0x563cbe9c3360]
/dlang/dmd/linux/bin64/../../src/phobos/std/range/primitives.d:2472 pure nothrow ref @property @nogc @safe inout(int) std.range.primitives.front!(int).front(return scope inout(int)[]) [0x563cbe9a0fe3]
/dlang/dmd/linux/bin64/../../src/phobos/std/range/primitives.d:297 pure nothrow @nogc @safe void std.range.primitives.doPut!(int[], int).doPut(ref int[], ref int) [0x563cbe9a0f62]
/dlang/dmd/linux/bin64/../../src/phobos/std/range/primitives.d:380 pure nothrow @nogc @safe void std.range.primitives.put!(int[], int).put(ref int[], int) [0x563cbe9a0f37]
./onlineapp.d:8 _Dmain [0x563cbe9a0ee1]
this is because put is there to write into a pre-allocated buffer if you pass in an array, as it assumes it is a slice:
int[3] buffer;
auto slice = buffer[];
put(slice, 1);
put(slice, 2);
put(slice, 3);
assert(!slice.length);
assert(buffer == [1,2,3]);
which seems to be the way this is intended to be used.
However now I argue this is very unintuitive behavior, especially when you compare it to appender!int:
auto arr = appender!(int[]);
arr.put(1);
assert(arr.data == [1]);
put on an appender actually adds to the array, the appender allocates memory for it.
I strongly feel that this behavior is very inconsistent and unexpected for most users and should be changed. I think we should deprecate simple arrays/slices on put and rename the method for those.
I propose put with slices should be renamed to putInto.
It might not be expected, but to disable allowing reference input ranges as output ranges would break so many fundamental usages, such as std.algorithm.copy. You wouldn't just be disabling slices, it would be a complete removal of a whole class of output ranges.
What we need is an appendTo wrapper:
struct AppendTo(T)
{
private T[] *arr;
this(return T[]* arr) { this.arr = arr; }
void put(X)(X val) if (__traits(compiles, (*arr) ~= val)) {
(*arr) ~= val;
}
}
auto appendTo(T)(return ref T[] arr)
{
return AppendTo!T(&arr);
}
-Steve
