Declaring and using a variable

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Declaring and using a variable

See also

Declaring and using a variable

Overview

A variable is defined by name and type.

The variable type defines the values that can be taken by the variable, its memory footprint and the available operations.

Reminder: Each type is identified by a WLanguage keyword. These keywords are reserved words.

This help page presents:

How to declare and initialize a variable,
How to access the properties of a variable,
The rules for variable scope.

To simplify the declaration of variables, you also have the ability to use the type inference.

How to declare a variable?

Declaring a variable

Declaring a variable and inializing it

Declaring several variables

Detailed syntaxes


<Variable name>:	Name of the variable to declare.
<Type>:	Type of the variable or type common to the declared variables (see Available types of variables).
<Initial value>:	Initial value of the variable (optional). This initial value depends on the type of variable.

Remarks:

The a and an keywords are optional: they provide better readability.
When several variables of the same type are declared and initialized on the same line, only the last variable is initialized.
To declare and initialize several variables at the same time, use the multiple initialization.
Several variables with the same name cannot be used in the same process (regardless of the type of these variables).
The "useful" attribute can be used when declaring a variable to specify that it is used in the project. This notation avoids displaying the warning indicating that a local variable is unused. In this case, the following syntax must be used:

<Variable name> is <Type>, useful[ = "Reason"]

<Variable name> is <Type> <useful [ = "Reason"]>

"Reason" is a note for the developer.
Example:

n1 is int, useful = "Variable required by the Webservice"

n2 is int <useful = "Variable required by the Webservice">

Examples

Declaring simple variables:

CustomerName is string
Counter is int
Price is real
i,j,k are int

The type inference allows you to use the following syntaxes:

let Amount = 1500.69 // real type
let City = "Montpellier" // string type
Declaring a Border variable:

MyBorder is Border

Declaring several variables and inializing them

<Variable name 1>, <Variable name 2>, ..., <Variable name N> are <Type>
= (<Initial value 1>, <Initial value 2>, ..., <Initial value M>)

Details of syntax


<Variable name>:	Name of the variable to declare. N represents the number of declared variables.
<Type>:	Type common to the declared variables (see Available types of variables).
<Initial value>:	Initial value of each variable. M represents the number of values to assign.

Remarks:

The assignments are performed from left to right.
If the number of variables is less than the number of values (N less than M), a compilation error will occur.
If the number of variables is greater than the number of values (N greater than or equal to M), only the first variables will be assigned.
You also have the ability to assign several variables with different values in a single line of code. For more details, see Multiple assignment.

Examples:

x, y, z are int = (1, 10, 4)
// x is set to 1, y to 10 and z to 4

s, t, p are strings = ("A", "B001")
// s is set to "A", t to "B001" and p to ""

Associating a critical section with a variable

When declaring a variable, this variable can be associated with a critical section by using the critical section attribute.

The syntax is as follows:

VariableName is VariableType <critical section>

or

VariableName is VariableType, critical section

The code sections that use these variables must be found between CriticalSectionStart and CriticalSectionEnd.

Special case: A critical section is automatically associated with the variables on which simple operations are performed, such as:

assigning a value.
retrieving a value.
incrementat, decrement (+, -, ++, --, +=, -= operators +, -, ++, --, += -=).

Example:

// Global declarations of WIN_STAT window
gcySum is currency, critical section
gcyMax is currency, critical section
...

// Code run by several threads
cyOrderAmount is currency
...
// atomic operation, the critical section is automatically managed by WLanguage
gcySum += cyAmountOrder

// multiple operation, it is necessary to implement the critical section explicitly
USING CriticalSection(gcyMax) IN
IF cyAmountOrder > gcyMax THEN
gcyMax = cyAmountOrder
END
END

Remarks:

The critical section attribute is allowed for:
- the global project variables, set of procedures, window, page and report.
- the local variables.
- the members of classes.
- the arrays: in this case, the attribute is associated with the array and not with the array elements.
The queues and the stacks are protected by default: the critical section attribute is not required.

How to access the properties of a variable?

Syntaxes

The following syntaxes can be used if the type of variable includes properties:

Assigning a property of the variable:

<Variable name>.<Property> = <Value>
Reading a property of the variable:

<Variable name>.<Property>

Example

Using properties on a Border type:

// Define the border characteristics
MyBorder is Border
MyBorder.Color = LightRed
MyBorder.Thickness = 5

Rule for variable scope

Rule

The rule for variable scope is as follows:

If a variable "global" to the project and a variable "global" to a window have the same name:
- the variable "global" to the window will be used in all the events or processes of the window and window controls as well as in its "local" procedures.
- the variable "global" to the project will be used in all the other processes.
If a variable "global" to the project and a variable "local" to a process have the same name:
- the "local" variable will only be used in the process where this variable was declared.
- the variable "global" to the project will be used in all the other processes.
If a variable "global" to a window and a variable "local" to a process of this window have the same name:
- the "local" variable will only be used in the process where this variable was declared.
- the variable "global" to the window will be used in all other events or processes of the window and its controls (as well as in its "local" procedures).
- none of these two variables can be used in the rest of the project.

Remark: The variables are specific to the executable, the Webservice or the WEBDEV session where they have been declared.

Compilation option
A compilation option is used to manage the scope of the local variables: Scope of local variables limited to the current block.

If this option is selected, the local variables will be specific to the block. You cannot use a local variable outside the block in which it is declared. The ending of the variable is run at the end of block (destructors and freeing memory).

You have the ability to redeclare a variable with the same name in two distinct sub-blocks but you cannot redeclare a variable with the same name in a child sub-block.

This option is selected by default for the new projects.

To modify this option:

Open the project description window: on the "Project" tab, in the "Project" group, click "Description".
In the "Compilation" tab, check or uncheck "Scope of local variables limited to the current block".

Exception

The rule for variable scope does not apply to the constants and to the Data Source variables.

Special case: Reports & Queries

The variables global to the project can be used in the reports and queries created and/or modified in "Reports & Queries".
The items for which "Visible to the end user in "Reports and Queries"" is checked in the data model editor can be used in "Reports and Queries". If this option is not checked, the item can only be used by indirection (the autocomplete feature is not available to the user, the item is not available in the wizards, description windows, etc.).

Name conflict: ambiguous use of a type

A WLanguage type can have the same name as another type added to the project by an imported element (.NET assembly classes, Webservice structured types, etc.). In this case, use the WL prefix to force the WLanguage type when declaring a variable.
Example:

// Force the use of the WLanguage XMLDocument type
// if the XMLDocument type exists elsewhere
MyVariable is WL.XMLDocument