Functional Programming
Functional Programming is not a fresh concept, such as C , although not a Functional Programming language, but it also has a variable support - Provide STL, Boost, etc. Smart, high performance algorithms and functions. These features that seem often to be C can be insulated for object-oriented programming languages and frameworks such as Java and C #. Now, in the support of the CLR model and C # 2.0 anonymous entrustment, we can also construct a surprising Functional Programming program, and more simple than C (of course, the performance cannot be compared, because the model in the CLR is a run Time technology, and the template in C is compiled technology). Current .NET BCL's support for Functional Programming is limited to the set class, which is exactly List
And array.
Let's take a simple example. Suppose there is a contact list List
The contact's definition is as follows:
Class Contact {
Public String Name;
...
}
Now we have to copy the name of all the contacts in this list to another list. You may immediately write it immediately:
List
C1 = ...;
List
C2 = new list
();
Foreach (Contact C IN C1) {
C2.Add (c.name);
}
This is a very rule of C # code. In .NET 2.0, there is a paradition and anonymous commission, we can write the implementation of the same function as follows:
List
C1 = ...;
List
C2 = c1.convertall
(
Delegate (Contact C) {return c.name;});
Obviously this code is more concisely than manually written Foreach code, and it is more clear and directly in the expression intent. Where the CONVERTALL method is a model method that converts the list element to a list of specified types. The prototype is:
List convertall (converter
CONVERTER);
Converter
It is a model delegate that specifies how to convert (similar to the function object in C ), the prototype is (T is the original type, U is the target type):
Delegate U Converter
(T from);
Here is just a simple example, for more complex situations, models and anonymous entrustments allow you to implement more imagination (for example, anonymous delegate allows you to reference the variables on the stack).
Below is the model delegate (located in the system namespace) in the BCL:
Prototype Description Delegate Bool Predicate
(T Obj);
When accessing a collection, an assertion of the specified element (TRUE or FALSE) DELEGATE VOID ACTION
When accessing the collection, make a specific action delegate int COMPARISON
(T x, t y);
Compare two elements DELEGATE U Converter
(T from);
Convert an element to another for copying elements between two collections
List
Methods of supporting Functional Programming:
Prototype Description INT Findex (Predicate
Match);
INT Findex (int index, predicate
Match);
INT Findex (int index, int count, predicate
Match);
Find the first index of the elements that meet the assertion conditions Int FindlastIndex (Predicate
Match);
INT FindlastIndex (int index, predicate
Match);
INT FindlastIndex (int index, int count, predicate
Match);
Find the last index of the elements that meet the assessment conditions List
Findall (Predicate
Match);
Find all elements that meet the assertion conditions Nullable
Find (Predicate
Match);
Find the first element NULLABLE
Findlast (Predicate
Find the last element BOOL EXISTS (Predicate
Match);
It is judged whether or not the elements that meet the assertion conditions have Bool TrueForll (Predicate
Match);
Judging whether all elements meet the assertion conditions Int Removeall (Predicate
Match);
Delete all elements that meet the assertion conditions, return to the number of elements of the delete void foreach (action
Action);
Similar to Foreach Statement Void Sort (Comparison
Comparison);
Sort List Convertall (Converter
CONVERTER);
Conversion set elements
The Array class provides a similar way to support Functional Programming, which is different from that are all types of methods and non-instance methods, which are limited to the space. Let's take a look at what the example is changed to an array:
Contact [] Contacts = ...;
String [] names = array.convertall
(Contacts,
Delegate (Contact C) {return c.name;});
