70-536 - Ch1 - Lesson 1 - Using Value types.

• .NET Framework (.NF) - an integral Windows component.
• Value types (VT) - simplest types in .NF.
• Contain their data directly - no ref to data stored elsewhere.
• Instances of VT stored on stack.
• 3 general VTs: built-in types, user-defined types, enumerations. Each is derived from System.ValueType.

Built-in VTs

• Base types, provided by .NF. Other types are built from these.
• Optimizing performance - runtime optimizes perf. of Int32 & UInt32. For F.P use Double.
• VTs function as objects - you can call methods on them (e.g. ToString() ).
• In .NT, all types are derived from System.Object.

Declaring VTs

• declare symbol as instance of that type.
• VTs - implicit constructor - declaring them instantiates the type automatically. (No ''new' keyword).
• Constructor assigns a default value to new instance (e.g. o or null).
• Best practice - explicitly initialize within declaration - bool b = false;
• C# is case-sensitive.
• Nullable - new type in .NF 2.0 - allows one to determine whether a value has been assigned or not.
• Nullable b = null;
• Shorthand - bool? b = null;
• HasValue and Value members - if (b.HasValue) ... else ...;

Creating User-Defined Types

• UDFs - structures/structs.
• structs - composite of other types - easier to work with related data.
• example - System.Drawing.Point.
• explicit construction - System.Drawing.Point p = new System.Drawing.Point(2,3);
• define own structures ~ struct keyword.
• Class/Struct - former created on heap & is ref type, latter created on stack & is VT.

Creating Enumerations

• Enums - related symbols that have fixed values.
• Use to provide a list of choices to developers using your class.
• E.g. - enum Titles : int { Mr, Ms, Mrs, Dr };
• Use when developers consuming your types must choose from a limited set of choices for a value.

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Structs

• struct - UDT. A lightweight class.
• similar - constructors, methds, fields, properties, operators,...
• diffs - dont support inheritance (cant inherit from any other class + implicitly sealed), or destructors. Class ref type, struct VT.
• structs - use only for types that are small, simple, and similar in behaviour and characteristics to built-in types.
• structs - > efficient in arrays, <>
• structs - can implement mult. interfaces.
• diffs - no custom default (i.e parameterless) constructor. Also cannot init. an instance fld in a struct (e.g. private int xVal = 50; )
• structs - can create without 'new' - though not recommended - more difficult to read.
• struct - override ToString() - prevents boxing. (e.g. when passing -> WriteLine() ).