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The ?.. (null-aware cascade) operator evaluates a sequence of operations on a target object only if that object is not null. If the target expression evaluates to null, the operator short-circuits, bypassing all subsequent cascaded operations, and yields null. If the target is non-null, it executes the operations and returns the original target object.

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Syntax

targetExpression
  ?..firstMember()
  ..secondMember = value
  ..thirdMember();

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Mechanics and Behavior

  • Short-circuiting: The null check occurs exactly once, at the evaluation of targetExpression. If targetExpression is null, the entire cascade block is skipped.
  • Single Application: The ?.. operator is only required for the first operation in the cascade sequence. Subsequent operations in the same chain use the standard cascade operator (..). The initial ?.. establishes the non-null guarantee for the remainder of the statement.
  • Return Value: Like the standard cascade operator, the return values of the individual methods or assignments within the cascade are discarded. The expression evaluates to a reference to the original targetExpression (or null).

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Execution Equivalency

To understand the underlying control flow, the null-aware cascade operator effectively desugars to a conditional block utilizing a temporary variable. 
// Using the null-aware cascade operator
var result = nullableObject
  ?..methodA()
  ..propertyB = 10;
The compiler treats the above expression as structurally equivalent to: 
// Underlying control flow
var _temp = nullableObject;
if (_temp != null) {
  _temp.methodA();
  _temp.propertyB = 10;
}
var result = _temp;

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Operator Precedence

The ?.. operator shares the same precedence level as the standard .. cascade operator.
  • Lower precedence than arithmetic, logical, and conditional operators: The target expression is naturally evaluated before the cascade begins. For example, a + b ?.. c() automatically evaluates as (a + b) ?.. c(), and a ? b : c ?.. d() evaluates as (a ? b : c) ?.. d(). Parentheses are not required to enforce this evaluation order.
  • Higher precedence than assignment operators: Cascade operators bind more tightly than assignment. Consequently, an expression like a = b ?.. c() evaluates as a = (b ?.. c()), applying the cascade operations to b before assigning the resulting reference to a.
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