"Ref Locals"

static void Test() {
	// Sets _matrices[_viewMatricesStartIndex + 3] to Matrix4x4.Identity
	ref var viewMatrix = ref GetMatrix(MatrixType.ViewMatrix, 3);
	viewMatrix = Matrix4x4.Identity;
	// We can dereference the reference and copy its value to a local here by using the standard local variable declaration syntax
	var projMatrix = GetMatrix(MatrixType.ProjectionMatrix, 2);
	projMatrix.M11 = 3f; // Changes only the local 'projMatrix', does not affect anything in _matrices

Code snippet taken from "Two Decades of C#: A Reference - C# 7".