GN: map strings to integers?

[Charles Nicholson]

Hi GN people!

In my project I'm building support for a number of different hardware versions of our firmware.

Each hardware version has a primary name, and that name maps to a unique integer (starting at 0, ascending). The integer is used both in the code as a -D definition, but then also as a build-time argument to other vendor-provided tools.

I'd love something like a map that I could simply import from a gni file into the various BUILD files that use it, but GN doesn't appear to have this. I could have the same cascading if/else logic everywhere, but that's not great when new hardware comes along.

I could do an exec_script into python and keep the dict in a central location, but exec_script isn't a feature we're supposed to sprint towards. So, before I do that, how do other people manage this? Are there any good patterns here?

Thanks in advance,

Charles

[Roland McGrath]

If you're happy to restrict the keys to strings of identifier characters ([A-Za-z0-9_]) that don't start with underscore, then you can use GN scopes for this.

```

  foo_map = {

    a = 1

    b = 2

   }

  foo_keys = [ "a", "b" ]

  foreach(key, foo_keys) {

    value = foo_map[key]

    defines += [ "${key}=${value}" ]

  }

```

There is no way to enumerate the scope, so you have to use a separate list like `foo_keys` above.

You can do fancier things by foregoing the dictionary-style lookup and just iterating over lists:

```

   foo_things = [

     { name = "a" value = 1 },

     { name = "b" value = 2 },

  ]

  foreach(thing, foo_things) {

    defines += [ "${thing.name}=${thing.value}" ]
  }

```

[Aaron Wood]

When I've wanted lookup-tables or other keyed maps, I've done the latter route that Roland suggests.

(but I also didn't know that you could index a scope with a string key like that...)

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[Charles Nicholson]

Ah, thanks Roland, that's very helpful and exactly what I think will help me here. I'll explore putting such a scope variable in a .gni file, and importing it where I need it.

Best,

Charles