generic + numeric + literals = abomination

[biozic]

Le 27/03/10 18:18, so a écrit :
> With this in mind, just one thing bugs me.
>
> ----
> import std.stdio;
>
> struct vector(T) {
> this(T m) { mm = m; }
> vector!T opBinary(string s)(T m) if(s=="*") {
> return vector!T(mm * m);
> }
> T mm;
> }
>
> void test(T)() {
> vector!T v = vector!T(0.5);
> vector!T u = v * 0.3;
> writeln("u: ", u.mm);
> }
>
> void main() {
> test!float();
> test!double();
> test!real();
> }
> -----
>
> This program compiles and runs just fine, but i feel dirty, you see I
> explicitly stated that opBinary takes a variable of type T,
> but it accepted 0.3 on all 3 tests, implicitly casted double to T. In
> C++ world this brings tons of trouble, especially performance problems,

In this case, when is(T==real), you could have a precision problem more 
than a performance problem. You lose less precision if you always use 
literals of the most precise type (eg 0.3L).

Performance problems could occur in C++ when your template type is 'long 
double' (?). But then if 'double' is the most efficient type and if you 
want performance, use it explictly everywhere.