To better illustrate my situation, I believe presenting it in code would be most effective:
interface IPluginSpec {
name: string;
state?: any;
}
interface IPluginOpts<PluginSpec extends IPluginSpec> {
name: PluginSpec['name'];
// How can we enforce the requirement of opts.initialState ONLY when PluginSpec['state'] has a value?
initialState: PluginSpec['state'];
}
function createPlugin<PluginSpec extends IPluginSpec>(
opts: IPluginOpts<PluginSpec>,
) {
console.log('create plugin', opts);
}
interface IPluginOne {
name: 'pluginOne';
// Ideally, we'd only have to define this if state is present or omitted entirely
// state: undefined;
}
// Error: Property 'initialState' is missing in type...
createPlugin<IPluginOne>({
name: 'pluginOne',
// How do we make initialState NOT mandatory?
// initialState: undefined,
// How can we prevent any non-undefined initialState values?
// initialState: 'anyvaluehere',
});
interface IPluginTwo {
name: 'pluginTwo';
state: number;
}
createPlugin<IPluginTwo>({
name: 'pluginTwo',
initialState: 0,
});