On 6/5/15 10:15 AM, Dennis Ritchie wrote:
On Friday, 5 June 2015 at 13:13:15 UTC, Steven Schveighoffer wrote:
string foo(string mode, string value)
{
return `writefln("mode ` ~ mode ~ `: %s", ` ~ value ~ `);`;
}
void main()
{
mixin(foo("Y", "3"));
mixin(foo("X", "2"));
}
Thanks. It looks really simple, but I still do not understand the
concept of using mixins in full.
I do not understand why in this line:
return `writefln("mode ` ~ mode ~ `: %s", ` ~ value ~ `);`;
use the following syntax:
~ mode ~ , ~ value ~
Because what foo is constructing is a string that makes sense in the
*caller*, not inside foo. What those statements do is concat the *value*
of mode (i.e. "Y" or "X") and the *value* of value (i.e. "3" or "2") to
the string.
It's equivalent to rust using the ${e} to do variable substitution.
For example, why here I can simply write:
void main() {
int b = 5;
mixin(`int a = b;`);
assert(a == 5);
}
Because b makes sense in the context of main.
Why should not I write like this:
void main() {
int b = 5;
mixin(`"int a = " ` ~ b ~ ` ";"`);
assert(a == 5);
}
Because it won't compile :) Mixin strings must be constructable at
compile time, the value of b depends on runtime. Not to mention that you
can't concat strings with ints.
-Steve
