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// If you'd write an actual function on a single line:
myCollection.Where(bool IsActive(MyObject x) { return x.IsActive; });

// Replace the {} with =>, the ; can then also be removed:
myCollection.Where(bool IsActive(MyObject x) => return x.IsActive);

// The return statement isn't necessary:
myCollection.Where(bool IsActive(MyObject x) => x.IsActive);

// Neither is a function name:
myCollection.Where(bool (MyObject x) => x.IsActive);

// Types can usually be inferred:
myCollection.Where((x) => x.IsActive);

// Remove redundant parenthesis:
myCollection.Where(x => x.IsActive);

// Example with multiple arguments, here you need parenthesis again:
myCollection.Where((x, y) => x.IsActive && y > 10);

// Sometimes the type can't be inferred:
myCollection.Where((MyObject x, int y) => x.IsActive && y > 10);

// You can (always) use full argument names if you like, although a single letter is common:
myCollection.Where((collectionItem, index) => collectionItem.IsActive && index > 10);

const auto& item = ... ;

Sander Rossel wrote:

Sometimes I think I've chosen the wrong profession