infer constructor type arguments from values

[kasperpeulen]

Would it be possible that strong mode infers the type of otherMap below to be Map<String, String>

  var map = new Map<String, String>();   
  var otherMap = new Map.from(map);

Now otherMap has type Map<dynamic, dynamic>.

[jmesserly]

@kasperpeulen definitely! We can use upwards inference for constructors like we do for generic methods. Was chatting with @leafpetersen earlier this week about this.

[kasperpeulen]

awesome 👍

[jmesserly]

BTW, a related issue is that we don't (AFAIK) do downwards inference on generic methods. Current state of the world:

• constructor type parameters are only inferred from downwards inference
• generic function type parameters are only inferred from upwards inference

[jmesserly]

Also map/list literals: dart-archive/dev_compiler#108
and block bodied lambda return: #25487

[jmesserly]

note, we should fix LUB first: #25802, or we're going to get strange results in some cases