Target Language Compiler

Record Aliases

In TLC it is possible to create what is called an alias to a record. Aliases are similar to pointers to structures in C. You can create multiple aliases to a single record. Modifications to the aliased record are visible to every place which holds an alias.

The following code fragment illustrates the use of aliases.

%createrecord foo { field 1 }
%createrecord a { }
%createrecord b { }
%createrecord c { }

%addtorecord a foo foo
%addtorecord b foo foo
%addtorecord c foo { field 1 }

%% notice we are not changing field through a or b.
%assign foo.field = 2

ISALIAS(a.foo) = %<ISALIAS(a.foo)>
ISALIAS(b.foo) = %<ISALIAS(b.foo)>
ISALIAS(c.foo) = %<ISALIAS(c.foo)>

a.foo.field = 2, %<a.foo.field>
b.foo.field = 2, %<b.foo.field>
c.foo.field = 1, %<c.foo.field>
%% note that c.foo.field is unchanged

It is possible to create aliases to records which are not attached to any other records, as in the following example.

%function func(value)
  %createrecord foo { field value }
  %createrecord a { foo foo }
ISALIAS(a.foo) = %<ISALIAS(a.foo)>
  %return a.foo
%endfunction

%assign x = func(2)
ISALIAS(x) = %<ISALIAS(x)>
x.field = %<x.field>

As long as there is some reference to a record through an alias, that record will not be deleted. This allows records to be used as return values from functions.

A qualified variable expressions references a variable in one of the following forms:

TLC Files