type 'int' is not a subtype of type 'double?'

[dhilshana]

This usually happens when an API response or data processing step returns an int value, but my model or function is expecting a double?.

When a double variable is assigned an int value, implicit conversion from int to double is possible. However, the mentioned error occurs in this case.

[dart-github-bot]

Summary: The issue arises when an API response or data processing step returns an integer value, but the code expects a nullable double. While implicit conversion from int to double is possible, the code throws an error in this scenario.

[jasimrazi]

I'm experiencing the same problem. Can you suggest a solution?

[mraleph]

Dart¹ does not implicitly coerce int to double (or vice versa), because (among other reasons) such conversions are not loss-less. You have to explicitly convert using num.toDouble() or num.toInt().

Footnotes

1. With the exception of JavaScript backend (dart2js) which uses JavaScript numbers to represent both int and double. ↩

[ulisseshen]

its confuse, because if you declare a variable as double my_double = 100; it will be acepted and no static erros will happen. It suggest to us that the same will work in the double.parse('100') when we received it from API or other data source.

[bwilkerson]

I can see how that can be confusing. It happens because of the following text in the language spec:

Let l be an integer literal that is not the operand of by a unary minus operator, and let T be the static context type of l. If double is assignable to T and int is not assignable to T, then the static type of l is double; otherwise the static type of l is int.

This means that an integer literal denotes a double when it would satisfy the type requirement, and an int would not. Otherwise it is an int, even in situations where that is an error.

That can make it seem as if Dart does coercions, but it doesn't, it just changes the interpretation of a numeric literal under one special condition.