📜 WAYPOINT LESSON

Lambda syntax and closures

⭐ beginner⏳ 13 min read📍 Lesson 63 of 85

A lambda is an inline method — and it captures the variables around it, for better and worse.

The forms

Func<int, int> square = x => x * x;              // expression lambda
Func<int, int> step  = x => { return x + 1; };   // statement lambda
Func<int, int> zero  = _ => 0;                   // ignore the parameter
Action shout = () => Console.WriteLine("hey!");  // no parameters

=> reads "goes to". The compiler infers parameter types from the delegate type. _ names a parameter you deliberately ignore.

Closures: lambdas remember

int offset = 10;
Func<int, int> shift = x => x + offset;   // captures offset
shift(5);   // 15

A lambda can use variables from the enclosing scope — the compiler wraps them into a hidden object so the lambda outlives the method call. That's a closure, and it's how Where(n => n > min) works: min travels with the lambda.

The classic trap: captured variables are shared, not copied. If offset changes later, shift sees the new value. And capturing a loop variable you mutate gives every lambda the same, final value.