LINQ study Note 3

Lambad Expression Tree:

There are two ways to compile the lamabda Expression Tree:

If the first parameter of the expression is declared as ienumberable <t> type, the compiler will compile it into the middle of Il.CodeWhen the extension method inherits from iqueryable <t>, the compiler generates an Expression Tree.

VaR keyword, anonymous type, object initialization

The VaR keyword allows us to initialize variables without knowing the variable type, such:

VaR A = new {name = 'zhang san', sex = 'mal '};

But Initialization is required.

VaR A; // compilation Error

 

Object initialization:

The traditional method is to first create an object and then initialize the object, for example

Address = new address ();
Address. Address = "105 Elm Street ";
Address. City = "Atlanta ";
Address. State = "Ga ";
Address. postalcode = "30339 ";

 

However, when it is an anonymous type, the above method will not be able to be initialized

For the anonymous type, the following initialization method is available.

VaR A = new {name = 'bar '};

 

Expansion Method:

Necessity of expansion method: 1. It is impossible to create an instance method with the same (similar) operation for each object

2. Static methods cannot meet all the conditions.

The so-called expansion method is the static method of the static class called on the instance.

 

For example:

Namespace Test
{
Public static class person
{
Public static string speak (this string words)
{
Return "this person said:" + words;
}
}
}

This is an extension method, which can be used in all string instances.

Note: 1. Reference The namespace where the expansion method you write is located.

2. Extension methods cannot be written in generic classes.

 

Priority: If you declare a tostring () Extension Method in the person class above, it cannot be called in the string instance.

Because the instance method has a higher priority than the extension method.