On Wednesday, 29 November 2017 at 06:18:09 UTC, Fra Mecca wrote:
I have this struct:
immutable struct Configuration {
string title;
string baseurl;
string url;
string email;
string author;
string parser;
string target;
string urlFormat;
string urlFormatCmd;
short port;
string[] ignore;
string[] extensions;
@property string toString()
{
auto urlF = (urlFormatCmd ? "url_format_cmd: " ~
urlFormatCmd : "") ~ "\n";
return
"title: " ~ title ~ "\n" ~
"baseurl: " ~ baseurl ~ "\n" ~
"url: " ~ url ~ "\n" ~
"email: " ~ email ~ "\n" ~
"author: " ~ author ~ "\n" ~
"parser: " ~ parser ~ "\n" ~
"target: " ~ target ~ "\n" ~
"url_format: " ~ urlFormat ~ "\n" ~
"ignore: " ~ to!string(ignore)[1 .. $ - 1] ~ "\n"
~
"extensions: " ~ to!string(extensions)[1 .. $ - 1] ~
"\n" ~
urlF;
}
}
and this function:
void show_config()
{
writef("%s", parse_config(
exists("config.sdl") ? "config.sdl" :
"").toString);
}
Whenever I compile with ldc2 I get no errors, while with dmd I
get:
source/configuration.d(105,27): Error: immutable method
configuration.Configuration.toString is not callable using a
mutable object
What is the problem?
You must also use a type constructor later, when a Configuration
is declared:
```
immutable(Configuration) config;
config.toString.writeln; // okay this time
```
What happens is that all the member functions have the
`immutable` attribute, but the instance you declared was not
itself `immutable`.
actually this:
```
immutable struct Configuration {
@property string toString(){return "";}
}
```
is like:
```
struct Configuration {
@property string toString() immutable {return "";}
}
```
I would personally prefer the second form. Why ? Because the
variable members will be set immutable anyway when an instance is
declared.
