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This article mainly introduces "what is C# pattern matching and how to achieve it". In daily operation, I believe that many people have doubts about what C# pattern matching has and how to realize it. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts of "what and how to achieve C# pattern matching"! Next, please follow the editor to study!

Pattern matching

To use pattern matching, you first need to understand what a pattern is. When using a regular expression to match a string, the regular expression itself is a pattern, and the process of matching a string using this regular expression is pattern matching. The same is true in the code, where the process of matching objects with a certain pattern is pattern matching.

There are many modes supported by C# 11, including:

Declaration mode (declaration pattern)

Type pattern (type pattern)

Constant mode (constant pattern)

Relational schema (relational pattern)

Logical pattern (logical pattern)

Attribute mode (property pattern)

Location mode (positional pattern)

Var mode (var pattern)

Discard mode (discard pattern)

List mode (list pattern)

Slice mode (slice pattern)

Among them, many patterns support recursion, which means that patterns can be nested to achieve more powerful matching functions.

Pattern matching can be used through switch expressions, as case in ordinary switch statements, or through is in if conditions. This article mainly uses pattern matching in switch expressions.

Then we will introduce these patterns.

Example: expression Calculator

In order to introduce pattern matching more intuitively, we next use pattern matching to write an expression calculator.

In order to write an expression calculator, we first need to abstract the expression:

Public abstract partial class Expr where T: IBinaryNumber {public abstract T Eval (params (string Name, T Value) [] args);}

We use the above Expr to represent an expression, where T is the type of Operand, and then further divide the expression into constant expression ConstantExpr, parameter expression ParameterExpr, unary expression UnaryExpr, binary expression BinaryExpr, and ternary expression TernaryExpr. Finally, an Eval method is provided to evaluate the value of the expression, which can be passed in an args to provide the parameters needed for the expression evaluation.

With unary and binary expressions, operators are naturally required, such as addition, subtraction, multiplication and division. We also define Operator to represent operators:

Public abstract record Operator {public record UnaryOperator (Operators Operator): Operator; public record BinaryOperator (BinaryOperators Operator): Operator;}

Then set the allowed operators, where the first three are unary operators, followed by binary operators:

Public enum Operators {[Description ("~")] Inv, [Description ("-")] Min, [Description ("!")] LogicalNot, [Description ("+")] Add, [Description ("-")] Sub, [Description ("*")] Mul, [Description ("/")] Div, [Description ("&")] And, [Description ("|")] Or, [Description ("^")] Xor, [Description ("=")] Eq, [Description ("! =")] Ne, [Description (">")] Gt, [Description ("=")] Ge [Description ("

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