Re: null as parametr

[Andrew Godfrey via Digitalmars-d-learn]

On Sunday, 31 July 2016 at 05:41:55 UTC, AntonSotov wrote:

2 Seb

Thank you!
is (T: typeof (null)) - very comfortable


An example of Seb's warning:
What happens if you have:
string s = null;
MyFunc(s);

I'm guessing it doesn't do what you want. But it isn't clear what 
you want - null is a value, not a type. It's just as if you were 
saying:

is (T: typeof (-3))

Re: null as parametr

[AntonSotov via Digitalmars-d-learn]

2 Seb

Thank you!
is (T: typeof (null)) - very comfortable

Re: null as parametr

[Seb via Digitalmars-d-learn]

On Sunday, 31 July 2016 at 05:22:40 UTC, AntonSotov wrote:

import std.stdio;

void myFunc(T)(in T val) {
static if(is(T == string)) {
writeln("string: ", val);
}
static if(is(T : long)) {
writeln("long: ", val);
}
static if // WHAT HERE ?
writeln("null");
}
}

int main(string[] args)
{
myFunc("abc");
myFunc(123);
myFunc(null);
return 0;
}
//--
How to transfer  as parameter type?


just have a look with pragma(msg, T) what the compiler is 
inferring ;-)
-> typeof(null) seems to be a Voldemord type that can't be 
expressed directly, hence you can do:


static if(is(T : typeof(null))) {
writeln("null");
}

... but does this really help you? A string can be null too, so 
whatever you do you most likely should check that with `val is 
null` too.

null as parametr

[AntonSotov via Digitalmars-d-learn]

import std.stdio;

void myFunc(T)(in T val) {
static if(is(T == string)) {
writeln("string: ", val);
}
static if(is(T : long)) {
writeln("long: ", val);
}
static if // WHAT HERE ?
writeln("null");
}
}

int main(string[] args)
{
myFunc("abc");
myFunc(123);
myFunc(null);
return 0;
}
//--
How to transfer  as parameter type?