• Alan Smith <alanrogersmith gmail.com> Dec 30 2007
• Matti Niemenmaa <see_signature for.real.address> Dec 30 2007

Alan Smith <alanrogersmith gmail.com> writes:

Hi,

I would like to know if it is possible to convert a char[] to a struct that has
a opCall(char[] str) function. For example:

import std.stdio;

char firstCharacterInString(pstring str)
{
    return str[0];
}


void main()
{
    writefln("first char = '%s'", firstCharacterInString("Hello World!")); //
should print "first char = 'H'"
}

pstring = http://www.dprogramming.com/dstring.php

The above code will output something like this:

Error: cannot implicitly convert expression ("Hello World!") of type char[12u]
to pstring

Is there any way to make D substitute "Hello World!" for pstring("Hello
World!")? How do I get the above code to work without creating an instance of
pstring like this:

pstring str = "Hello World!";

writefln("first char = '%s'", firstCharacterInString(str));

All help is appreciated!

Peace, Alan

Matti Niemenmaa <see_signature for.real.address> writes:

Alan Smith wrote:
 I would like to know if it is possible to convert a char[] to a struct that
 has a opCall(char[] str) function. For example:
 
 import std.stdio;
 
 char firstCharacterInString(pstring str) { return str[0]; }
 
 void main() { writefln("first char = '%s'", firstCharacterInString("Hello
World!")); // should print "first char = 'H'" }
 
 pstring = http://www.dprogramming.com/dstring.php
 
 The above code will output something like this:
 
 Error: cannot implicitly convert expression ("Hello World!") of type
 char[12u] to pstring
 
 Is there any way to make D substitute "Hello World!" for pstring("Hello
 World!")? How do I get the above code to work without creating an instance of
 pstring like this:
 
 pstring str = "Hello World!";
 
 writefln("first char = '%s'", firstCharacterInString(str));


You can't do it with structs, as far as I can tell.

If pstring were a class, you could do this:

import std.stdio;

class pstring {
	char[] foo;
	this(char[] s) {
		foo = s;
	}
}

// note the ellipsis
char firstCharacterInString(pstring str...) {
    return str.foo[0];
}

void main() {
    writefln("first char = '%s'", firstCharacterInString("Hello World!"));
}

Perhaps if, in the future, structs get constructors, you could do something like
this with structs.

Of course, you're free to make a wrapper class for your struct but that's
somewhat self-defeating in my opinion. :-)

-- 
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