Is there a way to get this associative array initialization to work?

[WhatMeWorry via Digitalmars-d-learn]

enum SoundType { MUSIC = 0, SOUND_EFFECT };

struct Sound
{
    string     file;
    SoundType  musicOrSfx;
    void*      ptr;   // Mix_Chunk* for sfx;  Mix_Music* for 
music;
}
immutable Sound[string] soundLibrary  =   // line 148
[
    "SCRATCH"          : { file : "scratch.wav", musicOrSfx : 
SOUND_EFFECT, ptr : null },
    "BACKGROUND_TRACK" : { file : "beat.wav",    musicOrSfx : 
MUSIC,        ptr : null },
    "HIGH"             : { file : "high.wav",    musicOrSfx : 
SOUND_EFFECT, ptr : null }	
];      


I keep getting a
source\app.d(148,1): Error: not an associative array initializer