On Thursday, 21 May 2015 at 11:16:47 UTC, ZombineDev wrote:
On Thursday, 21 May 2015 at 11:05:10 UTC, Dennis Ritchie wrote:
Is it possible to write something like this in the compile
time?
auto foo(T)(T t)
if (is(T == immutable(int)) && t == 5)
// Error: variable t cannot be read at compile time
{
// ...
}
void main()
{
immutable(int) n = 5;
foo(n);
}
Although the compiler already has enough information, this is
not possible because the template constraints are not allowed
to use the runtime parameters (they are compile-time only
constraints). It would be more doable like this:
auto foo(T)(T t)
if (is(T == immutable(int)))
{
assert(t == 5);
}
void main()
{
immutable int n = 6;
foo(n); // Possible in the future:
// dmd test.d --deep-asserts-verification
// Error: function foo has an assert which can't satisfied:
// assert(5 == n) <- n is 6
}
Yes, but I can do that I need check use strings ( source is taken
away http://ddili.org/ders/d.en/mixin.html ):
import std.conv : to;
import std.string : split;
import std.stdio : writeln;
int[] filter(string predicate)(in int[] numbers)
if (predicate.split[0] == "number" &&
predicate.split[1] == ">" &&
predicate.split[2].to!int <= int.max)
{
int[] result;
foreach (number; numbers) {
if (mixin (predicate)) {
result ~= number;
}
}
return result;
}
void main()
{
auto a = [1, 2, 3, 4, 5];
writeln(a.filter!"number > 3"); // [4, 5]
}
-----
http://rextester.com/LNTB90172
Code Ali is not safe, because I can refer to the inner filter
function directly in a function call :)
import std.conv : to;
import std.string : split;
import std.stdio : writeln;
int[] filter(string predicate)(in int[] numbers)
{
int[] result;
foreach (number; numbers) {
if (mixin (predicate)) {
result ~= number;
}
}
return result;
}
void main()
{
auto a = [1, 2, 3, 4, 5];
writeln(a.filter!"result != [1, 2]"); // [1, 2]
}
-----
http://rextester.com/LNTB90172
