Category Partial Types

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Partial Types

partial type Point
    x as long
    y as long
end type

partial type Point
    declare function Sum( ) as long
end type

function Point.Sum( ) as long
    return x + y
end function

dim as Point p = type( 3, 4 )
print p.Sum( )      ' 7

partial type writes one type in several blocks, and partial class does the same for a class. The compiler pools the blocks into a single type before anything else looks at it, so every other part of the language sees one ordinary type.

For the syntax on one page, see Partial.

Why It Exists

Some types have two authors. A form designer writes a form's controls and event declarations, and a person writes the form's own data and helper methods. With one block, the tool has to edit text the person owns. With two blocks, each keeps to its own, and the tool can rewrite its half at any time.

In a Module

The usual home for the parts is two files of one module. A module's files are compiled together, so its parts combine with no #include and no declare lines:

' frmMain/frmMain.design.tiko -- written by a tool
#module "frmMain"

public partial type Form
    btnOK as long
    declare sub btnOK_Click( )
end type

' frmMain/frmMain.tiko -- written by you
#module "frmMain"

partial type Form
    Count as long
end type

sub Form.btnOK_Click( )
    Count += 1
end sub

A program importing this module sees the whole type. sizeof( frmMain.Form ) counts the fields of both parts.

Rules

Every block says partial, and the same kind. A partial type and an ordinary type of the same name are an error, as are a partial type and a partial class.

All parts are in one compilation unit: one source file with its includes, or one module. They must be at module or namespace level, and in the same namespace.

Members combine in order. Fields are laid out part by part, in the order the compiler reads them. In a module that is the sorted order of its file names, which puts frmMain.design.tiko before frmMain.tiko. Declaring the same member in two parts is the usual "already declared" error.

One part may give each header clause. extends, field, extern layout and implements may each appear on one part, whichever part that is, and apply to the whole type. So may a class's inherits line; parts that write none take the base from the part that does. A base type's fields still come first.

Visibility. public on any part makes the type public, and the other parts need not repeat it. public on one part and private on another is an error.

A part can be methods alone. Only the whole type needs a field.

Not generic. A generic type cannot be partial.

partial is only a keyword directly before type or class. It remains an ordinary name everywhere else: dim as long partial and a procedure named partial are both fine.

Errors

Code	Means
TKO1063	One declaration says partial and another of the same name doesn't.
TKO1064	The type has type parameters.
TKO1065	partial is on an alias such as partial type T as long, which has no body.
TKO1066	Two parts give the same header clause.
TKO1067	One part is public and another private.
TKO1068	One part is a partial type and another a partial class.