C # generic constraints

This article will make a simple summary of the various types of generic constraints.

At the beginning of the article, a demo code manuscript is given (modified, demonstrated, and illustrated on this basis). ）

mylist<t> {    list<t> List = new list<t> ();    This.list[i] = value;} }}set;   }}

Next, modify the demo code manuscript to illustrate the different types of generic constraints.

1 specifying a generic parameter as a value type

T:struct{... Code omit part}

Look at the effect of adding a constraint, instantiate the MyList class as follows:

MyList<person> list = new MyList<person> ();   

You will notice that the following error message will be generated:

The type "Gencconstraint.person" must be a non-nullable value type to be used as the parameter "T" in the generic type or method "Gencconstraint.mylist<t>".

Instantiate the MyList class using the following method, and everything is OK:

mylist<new mylist<int> (); 

2 specifying a generic parameter as a reference type

T:class {... Code omit part}

After modifying a generic constraint to a reference type, the preceding error message disappears because the person class is a reference type that satisfies the generic constraint.

3 specifying a common constructor for a generic parameter with no arguments

T:new () {... Code omit part}

Add a private parameterless constructor for the person class with the following code:

person{person    (//do Nothing}} 

Instantiate MyList < person > class:

MyList<person> list = new MyList<person> ();   

A compilation error occurred, prompting:

"Gencconstraint.person" must be a non-abstract type with a public parameterless constructor before it can be used as a parameter "T" in a generic type or method "Gencconstraint.mylist<t>".

Haha, the restraints are working.

4 Specifies that generic parameters must be sent to the specified base class

Add abstract class Senioranimal

Senioranimal//Advanced Animal {    Speak ();  Usetool ();  will use the tool}     

Specifies that generic parameters must derive from the base class Senioranimal

senioranimal{... Code omit part}

Instantiate MyList < person > class (at this point the person class has not yet inherited from the Senioranimal Class):

MyList<person> list = new MyList<person> ();   

A compilation error occurred, prompting:

The type "Gencconstraint.person" cannot be used as a type parameter "T" in a generic type or method "Gencconstraint.mylist<t>". There is no implicit reference conversion from ' Gencconstraint.person ' to ' gencconstraint.senioranimal '.

Modify the code so that the person class inherits from the Senioranimal class

senioranimal{    Speak () {Console.WriteLine (Usetool () { Console.WriteLine ("I'll use a machete!" "); }}

Compile again, everything is OK.

5 specifies that the generic parameter must implement the specified interface

If the demo is similar to the 4th, no demo code is provided.

6 specifies that generic parameters must be sent to the generic type U (bare type constraint)

mylist<void showinfo<t> () where T:u {}}

In addition, you can apply multiple constraints to the same generic parameter.

All right, Game over!.

C # generic constraints