unused_result

'{0}' should be used. {1}.

The value of '{0}' should be used.

The analyzer produces this diagnostic when a function annotated with useResult is invoked, and the value returned by that function isn't used. The value is considered to be used if a member of the value is invoked, if the value is passed to another function, or if the value is assigned to a variable or field.

The following code produces this diagnostic because the invocation of c.a() isn't used, even though the method a is annotated with useResult:

import 'package:meta/meta.dart';

class C {
  @useResult
  int a() => 0;

  int b() => 0;
}

void f(C c) {
  c.a();
}

If you intended to invoke the annotated function, then use the value that was returned:

import 'package:meta/meta.dart';

class C {
  @useResult
  int a() => 0;

  int b() => 0;
}

void f(C c) {
  print(c.a());
}

If you intended to invoke a different function, then correct the name of the function being invoked:

import 'package:meta/meta.dart';

class C {
  @useResult
  int a() => 0;

  int b() => 0;
}

void f(C c) {
  c.b();
}