.?? support for Streamlined Null-Coalescing and Type-Casting

[BN-KS]

Summary

Introduce support for .?? operator to streamline null-coalescing within conditional expressions, reducing the need for parentheses and minimizing coding friction. This feature would simplify scenarios where developers combine null-conditional (?.) and null-coalescing (??) logic, improving code readability and flow.

Motivation

Today, developers often encounter syntactic friction when combining ?. and ?? in expressions. For example when writing:
if (someCondition || someOtherCondition?.couldExist ?? false...
You have to jump back to enclose the latter condition:
if (someCondition || (someOtherCondition?.couldExist ?? false)) { }
The need to jump back and insert parentheses before and after interrupts the natural flow of coding. This can break focus, slow productivity, and increase the likelihood of introducing subtle errors. Supporting ".??" would eliminate this friction, allowing for:
if (someCondition || someOtherCondition?.couldExist.??false) { }
This syntax preserves readability and reduces interruptions, making it easier to write and maintain code.

Benefits

Improved developer productivity: Reduces the need for manual parenthesis adjustments.
Minimized cognitive load: Keeps the focus on the logic, not syntax.
Cleaner code: More concise and expressive syntax for common patterns.

Proposed Behavior

The .?? operator would combine the ?. and ?? behaviors, applying null-coalescing directly to the result of a null-conditional access. It would function equivalently to:
(someOtherCondition?.couldExist ?? false)
But with simpler syntax:
someOtherCondition?.couldExist.??false

Considerations

Backward compatibility: The .?? operator is new syntax and would not conflict with existing code.
Learning curve: The feature aligns naturally with existing null-coalescing and null-conditional patterns.

Extended Proposed Feature: .??<type>

Further extending ".??" to support type casting could look like this:
if (something && something.That.Could.Be.Int.??int == 42) { }
The .?? operator would attempt to cast the value to the specified type, falling back to default(type) if the cast fails.
if (true && somethingThatCouldBe?.Value.??int == 42) { }
Equivalent to:
if (true && (somethingThatCouldBe?.Value as int? ?? default(int)) == 42) { }

Advantages of .??

Streamlined syntax: Eliminates the need for parentheses or temporary variables.
Default fallback: Automatically handles null and invalid cast cases.
Consistency: Builds upon the .?? operator for null-coalescing, creating a unified pattern.

Alternative Solution: Compiler Change

An alternative to introducing new syntax is relaxing the compiler precedence rules to implicitly group null-handling logic when && or || is used. For example:
if (true && somethingThatCouldBe?.BoolOrNull ?? false) { }
The compiler could implicitly interpret this as:
if (true && (somethingThatCouldBe?.BoolOrNull ?? false)) { }
This avoids the need for new syntax while preserving backwards compatibility.

Benefits of .?? and .??

Developer Productivity: Reduces interruptions by eliminating parentheses in null-handling and casting scenarios.
Unified Syntax: Aligns with existing ?. and ?? operators, building on familiar patterns.
Enhanced Readability: Concisely expresses logic without obscuring intent.
Backward Compatibility: Introduces no breaking changes, as .?? and .?? are new constructs.

Conclusion

The .?? operator is a small but meaningful enhancement to C# that aligns with the language’s goals of developer productivity and code clarity. By reducing friction during the coding process, it helps programmers focus on their stream of logic rather than on syntax.