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C# 3.0 introduced type inference, allowing the type specifier of a variable declaration to be replaced by the keyword var, if its actual type can be statically determined from the initializer. This reduces repetition, especially for types with multiple generic type-parameters , and adheres more closely to the DRY principle.
The specification for pass-by-reference or pass-by-value would be made in the function declaration and/or definition. Parameters appear in procedure definitions; arguments appear in procedure calls. In the function definition f(x) = x*x the variable x is a parameter; in the function call f(2) the value 2 is the argument of the function. Loosely ...
However, within C# value types, this has quite different semantics, being similar to an ordinary mutable variable reference, and can even occur on the left side of an assignment. One use of this in C# is to allow reference to an outer field variable within a method that contains a local variable that has the same name.
A reference variable, once declared and bound, behaves as an alias of the original variable, but it can also be rebounded to another variable by using the reference assignment operator = ref. The variable itself can be of any type, including value types and reference types, i.e. by passing a variable of a reference type by reference (alias) to ...
Type inference – C# 3 with implicitly typed local variables var and C# 9 target-typed new expressions new List comprehension – C# 3 LINQ; Tuples – .NET Framework 4.0 but it becomes popular when C# 7.0 introduced a new tuple type with language support [104] Nested functions – C# 7.0 [104] Pattern matching – C# 7.0 [104]
This function has a side-effect – modifies the value passed by address to the input value plus 2. It could be called for variable v as addTwo(&v) where the ampersand (&) tells the compiler to pass the address of a variable. Giving v is 5 before the call, it will be 7 after.
because the argument to f must be a variable integer, but i is a constant integer. This matching is a form of program correctness, and is known as const-correctness.This allows a form of programming by contract, where functions specify as part of their type signature whether they modify their arguments or not, and whether their return value is modifiable or not.
Some languages assist this task by offering constructs to handle the initializedness of variables; for example, C# has a special flavour of call-by-reference parameters to subroutines (specified as out instead of the usual ref), asserting that the variable is allowed to be uninitialized on entry but will be initialized afterwards.