Cleverness of the compiler

[growler]

On Monday, 25 November 2013 at 00:51:47 UTC, growler wrote:
> On Monday, 25 November 2013 at 00:08:52 UTC, Namespace wrote:
>> I love this feature, but I'm unsure how it works. Can someone 
>> explain me, how the compiler deduce that he should read 4 
>> bytes for each index (the 'at' function)? The type is void*, 
>> not int*.
>>
>> ----
>> import std.stdio;
>> import core.stdc.stdlib : calloc, realloc, free;
>> import core.stdc.string : memcpy;
>>
>> struct Tarray {
>> 	void* ptr;
>> 	size_t length;
>> 	size_t capacity;
>>
>> 	~this() {
>> 		.free(this.ptr);
>> 		this.ptr = null;
>> 	}
>> }
>>
>> void push(T)(ref Tarray arr, T elem) {
>> 	if (arr.length == arr.capacity)
>> 		arr.reserve(T.sizeof);
>>
>> 	memcpy(&arr.ptr[arr.length++], &elem, T.sizeof);
>> }
>>
>> void reserve(ref Tarray arr, size_t typeOf, size_t cap = 0) {
>> 	if (arr.capacity != 0) {
>> 		arr.capacity = cap == 0 ? (arr.capacity * 2) + 1 : 
>> arr.capacity + cap;
>> 		arr.ptr = .realloc(arr.ptr, arr.capacity * typeOf);
>> 	} else {
>> 		arr.capacity = cap == 0 ? 3 : cap;
>> 		arr.ptr = .calloc(arr.capacity, typeOf);
>> 	}
>> }
>>
>> void at(T)(ref Tarray arr, size_t index, T* elem) {
>> 	if (index >= arr.length || elem is null)
>> 		return;
>>
>> 	memcpy(elem, &arr.ptr[index], T.sizeof);
>> }
>>
>> void main() {
>> 	Tarray arr;
>> 	arr.push(42);
>> 	int a;
>> 	arr.at(0, &a);
>> 	writeln(a, "::", arr.length, "::", arr.capacity);
>> 	arr.push(23);
>> 	arr.at(1, &a);
>> 	writeln(a, "::", arr.length, "::", arr.capacity);
>> 	arr.push(1337);
>> 	arr.at(2, &a);
>> 	writeln(a, "::", arr.length, "::", arr.capacity);
>> 	arr.push(ushort.max + 1);
>> 	arr.at(3, &a);
>> 	writeln(a, "::", arr.length, "::", arr.capacity);
>> }
>> ----
>
> All the calls to 'at' are using T=int (implied), as far as I 
> can tell.
> ...
> int a;
> ...
> arr.at(0, &a); // tyepof(a) is int so in 'at' T.sizeof = 4.
>
> Is this the call to 'at' you're referring to?
>
> Cheers

Sorry, T=int should be T=int*