Why 2.0 (the number 2.0) is double and int at the same time?

问题

I just started to learn Dart and came across the below code

main(){
  print(2.0 is int);
  print(2.0 is double);
  print(int is double);
}

It produces the below output

true
true
false

I am not sure why the above output is generated. The above output suggests that all integers can be treated as doubles.

Am I missing something obvious here. Any pointers would help. Thanks.

回答1:

You can only get this result if you run the code in the browser.

The browser does not distinguish between int and double, and knows only double, and therefore Dart also can not distinguish between them when compiled to JS.

Theoretically it would be possible but the performance penalty for using a custom type to maintain the integer properties would be prohibitively high.

See also https://webdev.dartlang.org/faq#q-how-are-integers-handled-when-compiled-to-javascript

来源：https://stackoverflow.com/questions/54827376/why-2-0-the-number-2-0-is-double-and-int-at-the-same-time