How can i get the value from an enum when passed to a function?

[Gary Willoughby]

How can i get the value from an enum when passed to a function? 
For example i have the following code:


import std.stdio;

enum E : string
{
one = "1",
two = "2",
}

void print(E e)
{
writefln("%s", e);
}

void main(string[] args)
{
print(E.one);
}

The output is 'one'. How can i get at the value '1' instead. I 
could change the print function to accept a string like this:


void print(string e)
{
writefln("%s", e);
}

but i lose the constraint of using an enum for the values.

Re: How can i get the value from an enum when passed to a function?

[Jakob Ovrum]

On Sunday, 19 January 2014 at 18:07:46 UTC, Tobias Pankrath wrote:
You'll need to cast the value, but you can guard this cast 
using std.traits.OriginalType or write a toOType function.


auto toOType(E)(E e) if(is(E == enum)) { return 
cast(OriginalType!E) e; }


I never get these is-expressions right on first try, but the 
idea should be clear.


You don't have to use an explicit cast. Enum values can be 
implicitly converted to their base enum type:


---
string str = E.one;
writeln(str); // prints "1"
---

If DMD pull request #1356[1] is pulled, I think we'll be able to 
do:


---
writeln(string(E.one)); // prints "1"
---

I recommend avoiding the cast operator whenever possible.

[1] https://github.com/D-Programming-Language/dmd/pull/1356

Re: How can i get the value from an enum when passed to a function?

[Tobias Pankrath]

On Sunday, 19 January 2014 at 17:37:54 UTC, Gary Willoughby wrote:
How can i get the value from an enum when passed to a function? 
For example i have the following code:


import std.stdio;

enum E : string
{
one = "1",
two = "2",
}

void print(E e)
{
writefln("%s", e);
}

void main(string[] args)
{
print(E.one);
}

The output is 'one'. How can i get at the value '1' instead. I 
could change the print function to accept a string like this:


void print(string e)
{
writefln("%s", e);
}

but i lose the constraint of using an enum for the values.


You'll need to cast the value, but you can guard this cast using 
std.traits.OriginalType or write a toOType function.


auto toOType(E)(E e) if(is(E == enum)) { return 
cast(OriginalType!E) e; }


I never get these is-expressions right on first try, but the idea 
should be clear.