Csc153 chapter 08
- 1. Microsoft Visual C# 2010 Fourth Edition Chapter 8 Advanced Method Concepts
- 2. Objectives • Learn about parameter types: ref parameters, out parameters, and parameter arrays • Overload methods • Learn how to avoid ambiguous methods • Use optional parameters Microsoft Visual C# 2010, Fourth Edition 2
- 3. Understanding Parameter Types • Mandatory parameter – Argument for it is required in every method call • Four types of mandatory parameters – Value parameters • Declared without any modifiers – Reference parameters • Declared with the ref modifier – Output parameters • Declared with the out modifier – Parameter arrays • Declared with the params modifier Microsoft Visual C# 2010, Fourth Edition 3
- 4. Using Mandatory Value Parameters • Value parameter – Method receives a copy of the value passed to it – Copy is stored at a different memory address than actual parameter • Changes to value parameters never affect the original argument in the calling method Microsoft Visual C# 2010, Fourth Edition 4
- 5. Using Value Parameters (cont'd.) Microsoft Visual C# 2010, Fourth Edition 5
- 6. Using Reference and Output Parameters • Reference and output parameters – Have memory addresses that are passed to a method, allowing it to alter the original variables • Differences – Reference parameters need to contain a value before calling the method – Output parameters do not need to contain a value • Reference and output parameters act as aliases – For the same memory location occupied by the original passed variable Microsoft Visual C# 2010, Fourth Edition 6
- 7. Using Reference and Output Parameters (cont'd.) Microsoft Visual C# 2010, Fourth Edition 7
- 8. Using Reference and Output Parameters (cont'd.) Microsoft Visual C# 2010, Fourth Edition 8
- 9. Using Reference and Output Parameters (cont'd.) • Advantage of using reference and output parameters – Method can change multiple variables • Disadvantage to using reference and output parameters – Allow multiple methods to have access to the same data, weakening the “black box” paradigm Microsoft Visual C# 2010, Fourth Edition 9
- 10. Using Parameter Arrays • Parameter array – A local array declared within the method header by using the keyword params – Used when you don’t know how many arguments of the same type you might eventually send to a method • No additional parameters are permitted after the params keyword • Only one params keyword is permitted in a method declaration Microsoft Visual C# 2010, Fourth Edition 10
- 11. Using Parameter Arrays (cont'd.) Microsoft Visual C# 2010, Fourth Edition 11
- 12. Overloading Methods • Overloading – Involves using one term to indicate diverse meanings • When you overload a C# method: – You write multiple methods with a shared name – Compiler understands your meaning based on the arguments you use with the method • Methods are overloaded correctly when: – They have the same identifier but parameter lists are different Microsoft Visual C# 2010, Fourth Edition 12
- 13. Overloading Methods (cont'd.) Microsoft Visual C# 2010, Fourth Edition 13
- 14. Overloading Methods (cont'd.) Microsoft Visual C# 2010, Fourth Edition 14
- 15. Microsoft Visual C# 2010, Fourth Edition 15
- 16. Understanding Overload Resolution • Overload resolution – Used by C# to determine which method to execute when a method call could execute multiple overloaded method • Applicable methods – Set of methods that can accept a call with a specific list of arguments • Betterness rules – Rules that determine which method version to call – Similar to the implicit data type conversion rules Microsoft Visual C# 2010, Fourth Edition 16
- 17. Understanding Overload Resolution (cont'd.) Microsoft Visual C# 2010, Fourth Edition 17
- 18. Understanding Built-In Overloaded Methods • When you use the IDE to create programs: – Visual Studio’s IntelliSense features provide information about methods you are using Microsoft Visual C# 2010, Fourth Edition 18
- 19. Avoiding Ambiguous Methods • Ambiguous method – Compiler cannot determine which method to use – Occurs when you overload methods • Methods with identical names that have identical parameter lists but different return types – Are not overloaded Microsoft Visual C# 2010, Fourth Edition 19
- 20. Avoiding Ambiguous Methods (cont'd.) Microsoft Visual C# 2010, Fourth Edition 20
- 21. Using Optional Parameters • Optional parameter – One for which a default value is automatically supplied • Make a parameter optional by providing a value for it in the method declaration – Only value parameters can be given default values • Any optional parameters in a parameter list must follow all mandatory parameters Microsoft Visual C# 2010, Fourth Edition 21
- 22. Using Optional Parameters (cont'd.) Microsoft Visual C# 2010, Fourth Edition 22
- 23. Using Optional Parameters (cont'd.) Microsoft Visual C# 2010, Fourth Edition 23
- 24. Leaving Out Unnamed Arguments • When calling a method with optional parameters (and you are using unnamed arguments) – Leave out any arguments to the right of the last one you use Microsoft Visual C# 2010, Fourth Edition 24
- 25. Leaving Out Unnamed Arguments (cont'd.) Microsoft Visual C# 2010, Fourth Edition 25
- 26. Using Named Arguments • In C# 4.0, leave out optional arguments in a method call – If you pass the remaining arguments by name • Named arguments appear in any order – But must appear after all the unnamed arguments have been listed • Name an argument using its parameter name and a colon before the value Microsoft Visual C# 2010, Fourth Edition 26
- 27. Using Named Arguments (cont'd.) Microsoft Visual C# 2010, Fourth Edition 27
- 28. Overload Resolution with Named and Optional Arguments • Named and optional arguments affect overload resolution – Rules for betterness on argument conversions are applied only for arguments that are given explicitly • If two signatures are equally good – Signature that does not omit optional parameters is considered better Microsoft Visual C# 2010, Fourth Edition 28
- 29. You Do It • Activities to explore – Using Reference Parameters – Overloading Methods Microsoft Visual C# 2010, Fourth Edition 29
- 30. Summary • Method parameters can be mandatory or optional • Types of formal parameters – Value parameters – Reference parameters – Output parameters – Parameter arrays • When you overload a C# method, you write multiple methods with a shared name – But different argument lists Microsoft Visual C# 2010, Fourth Edition 30
- 31. Summary (cont'd.) • When you overload a method, you run the risk of creating an ambiguous situation • An optional parameter to a method is one for which a default value is automatically supplied – If you do not explicitly send one as an argument Microsoft Visual C# 2010, Fourth Edition 31