Category:Elena: Difference between revisions

ELENA does not support multiple inheritance, though it is possible to inherit the code using redirect handler (so called "horizontal inheritance"). When the parent is not provided the class inherits directly system'Object (the super class).

 

{

}

{

[

theField1 := aField1.

]

= MyClass new &Field1:(theField1 + aField1) &Field2:(theField2 + aField2).

}

To create a class instance we have to send a message (usually new) to its symbol (a class symbol is declared implicitly for every class and can be used as a normal one)

 

 

 

{

}

...

 

In general the symbol is a named expression and can be used to declare initialized objects, constants, reusable expressions and so on.

 

 

A static symbol is the class instance which state is preserved. There could be only one instance of static symbol.

 

 

== Code blocks ==

ELENA code block consists of a sequence of statements. The block is enclosed in square brackets and may contain nested sub code blocks (which in fact are inline action classes). The statement terminator is a dot.

 

[

control forrange &int:0 &int:n &do: (&int:i)

If the code block contains only return statement the simplified syntax can be used:

 

 

or there is an alternative block expression

It is possible to declare the block variable and assigns the value to it. The variable name must be unique within the code block scope.

 

 

 

ELENA like Smalltalk does not support any special language constructs to implement the conditional branching. Instead special Boolean symbols (system’true and system’false) are used. All conditional operations should return these symbols as a result.

 

 

[

n + 1

]

m + n

].

Note that code in square brackets are in fact nested action classes ( an action class is a class supporting evaluate message). So this code is can be written in this form:

 

{

eval

]

}

eval

[

]

! [

]