Suggestion to avoid allocations by passing delegate directly or lambda #3761
Description
The aim of dotnet/roslyn#40364 is simplification, while the aim of this alternative is performance.
↓ denotes where the suggestion span would be and _ denotes the spans that would be faded as unnecessary.
class C
{
// Changed to an instance method because of https://github.com/dotnet/roslyn/pull/58288
bool IsEven(int x) => x % 2 == 0;
void Example1()
{
// 💡 Avoid allocation by replacing method group with lambda
// ↓↓↓↓↓↓
_ = new[] { 1, 2, 3 }.Where(IsEven);
// 🛠 Fix result:
_ = new[] { 1, 2, 3 }.Where(n => IsEven(n));
}
void Example2()
{
var neverReassigned = new Func<int, bool>(IsEven);
// 💡 Avoid allocation by replacing lambda with delegate
// _____↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓___
_ = new[] { 1, 2, 3 }.Where(n => neverReassigned(n));
// 💡 Avoid allocation by replacing lambda with delegate
// _____↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓__________
_ = new[] { 1, 2, 3 }.Where(n => neverReassigned.Invoke(n));
// 💡 Avoid allocation by replacing Invoke method group with delegate
// ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓_______
_ = new[] { 1, 2, 3 }.Where(neverReassigned.Invoke);
// 🛠 Fix result:
_ = new[] { 1, 2, 3 }.Where(neverReassigned);
}
void Example3()
{
var reassigned = new Func<int, bool>(IsEven);
// No diagnostic
_ = new[] { 1, 2, 3 }.Where(n => reassigned.Invoke(n));
// 💡 Avoid allocation by replacing Invoke method group with delegate
// ↓↓↓↓↓↓↓↓↓↓_______
_ = new[] { 1, 2, 3 }.Where(reassigned.Invoke);
reassigned = n => !IsEven(n);
// 🛠 Fix result:
_ = new[] { 1, 2, 3 }.Where(reassigned);
}
}