On 03/15/2017 08:27 PM, WhatMeForget wrote:
>
> One of my D books says: "an enum declared without any braces is called a
> manifest constant." The example shows,
>
> enum string author = "Mike Parker";
>
> Is this equivalent to
> const string author = "Mike Parker";
> or
> immutable string author = "Mike Parker";
>
> I guess what I'm asking is does enum give you some advantages over say
> non-enum constants?
The guideline should be, "prefer enum except when the type is an array
except if it's a string." :)
You can think of enum as a text replacement similar to C macros.
Whenever you see 'author' in code, it would be as if it was replaced
with its value:
writeln(author);
writeln("Mike Parker"); // Same as above
The limitation is that just like you cannot take the address of e.g. 42,
you can't take the address of an enum:
// All lines below are compilation errors: "not an lvalue"
writeln(&42);
writeln(&"Mike Parker");
writeln(&author);
const static and immutable have the advantage of being initialized at
runtime. This one reads the name from a file:
import std.stdio;
immutable string author;
string makeAuthor() {
import std.file;
auto content = read("author_name_file");
return cast(string)content;
}
shared static this() {
author = makeAuthor();
}
void main() {
writeln(author);
}
Ali
