Dart Null-Aware Access

expression?.member

String? text = null;

// Evaluates to null. 
// Semantically equivalent to: text == null ? null : text.length
int? length = text?.length; 

List<int>? numbers = null;

// Evaluates to null. The add() method is never executed.
// The static type of this expression is void.
numbers?.add(1); 

class C {
  int value = 42;
}

class B {
  C? c;
}

class A {
  B? b;
}

A? a = A();

// 'a' is non-null, but 'a.b' is null. 
// The chain short-circuits at 'a?.b', returning null.
// The accesses for 'c' and 'value' are never attempted.
int? result = a?.b?.c?.value; 

class Bar {
  int c = 42;
}

class Foo {
  Bar b = Bar(); // Statically non-nullable
}

Foo? obj = null;

// Valid syntax. The chain short-circuits at 'obj?.'.
// The standard '.' before 'c' is never evaluated at runtime.
// This compiles strictly because 'b' is declared as non-nullable in 'Foo'.
int? val = obj?.b.c;