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digitalmars.D.learn - Implicit conversion of char[] to string struct

reply 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
Dec 30 2007
parent 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. :-) -- E-mail address: matti.niemenmaa+news, domain is iki (DOT) fi
Dec 30 2007