Advanced Programming Techniques in D/

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const, enum, immutable, and bool Conversions

const, enum, immutable, and bool Conversions

Learn about const, enum, immutable, and bool conversions.

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const conversions

As you know, reference types can automatically be converted to the const of the same type. Conversion to const is safe because the width of the type does not change and const is a promise to not modify the variable:

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D
import std.stdio;
char[] parenthesized(const char[] text) {
    return "{" ~ text ~ "}"; 
}
void main() {
    char[] greeting;
    greeting ~= "hello world";
    write(parenthesized(greeting));
}

The mutable greeting above is automatically converted to a const char[] as it is passed to parenthesized().

As you have also seen earlier, the opposite conversion is not automatic. A const reference is not automatically converted to a mutable reference:

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D
import std.stdio;
char[] parenthesized(const char[] text) {
    char[] argument = text; // ← compilation ERROR
    return argument;
}
void main() {
    char[] greeting;
    greeting ~= "hello world";
    write(parenthesized(greeting));
}

Note that this topic is only about references. Since variables of value types are copied, it is not possible to affect the original ...