Where Clause (Generics)

Specifies constraints to put on generic parameters.

Syntax

Where constraint [ , constraint ]…

Parts

constraint

One or more constraints to put on a generic parameter, with a comma between each.

Constraint

Long construct	Short construct
[ min_type { < | <= } ] type_parameter { < | <= } max_type	[ min_type { < | <= } ] type_parameter [ { < | <= } max_type ]
type_parameter Is { Class | Struct | Unit }	[ Is { Class | Struct | Unit } ]
type_parameter Does mandatory_trait	[ Does mandatory_trait ]…
type_parameter Constructor ( )	[ Constructor ( ) ]
Self { < | <= | Is } self_type	(Not available)

Short construct
[ min_type { < | <= } ] type_parameter [ { < | <= } max_type ] [ Is { Class | Struct | Unit } ] [ Does mandatory_trait ]… [ Constructor ( ) ]

type_parameter

One of the generic parameters given in a Type List.

max_type

The most basic class from which type_parameter can inherit. Use < if type_parameter must be a child of max_type, or <= to include max_type also.

min_type

The most specialized class from which type_parameter can inherit. Use < if type_parameter must be a child of min_type, or <= to include min_type also.

mandatory_trait

A trait that type_parameter must implement.

Is

Specifies that type_parameter must be one of these:

• A reference type (Is Class)
• A value type (Is Struct)
• A unit of measure (Is Unit)

Constructor

Specifies that type_parameter must supply a default constructor.

self_type

A class from which the applicable class must inherit. This constraint is available to classes and traits only.

Instructions

TODO

Examples

Class Dictionary[DataType, KeyType]
  Where KeyType Does Compare Constructor()

  Method Add d As DataType, k As KeyType
  End Method
  Method Find(k As KeyType) As DataType
  End Method
End Class

Applies to

• Class Statement
• Event Statement
• Function Statement
• Method Statement
• Struct Statement
• Sub Statement
• Trait Statement

See also

• Constructor Statement
• Generic Types
• Type List