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AL variables

  • Articolo

AL has the following types of variables:

  • User-defined variables
  • System-defined variables

User-defined variables are variables that you define when you create new AL code. You can define variables that are global and apply to all methods in an object, such as a codeunit, or you can define variables that are local and apply to a single method in an object. Both types of user-defined variables are local to the object in which they're defined. These variables can be used to store information at runtime, and the values can be changed as desired.

System-defined variables are provided by Business Central. These variables are automatically maintained by the system. Some system-defined variables are Rec, xRec, CurrPage, and CurrReport. For more information, see System-defined variables.

At runtime, code is run in methods and triggers, such as in entry-processing code for a table. Before the code is run, values are automatically assigned to the associated system-defined variables, and the values of these variables can be used in triggers and local methods.

The values of system-defined variables aren't updated when the AL code is being run. Instead, the values are updated before the method or trigger is run.

Note

The value in a system-defined variable doesn't propagate backward. A user can't use a system-defined variable to modify the state of the system.

Variable names

You must follow the following rules and restrictions when you name variables:

  • Variable names must be unique. A codeunit can't contain two user-defined variables with the same name in the same scope. You can have a local variable and a global variable with the same name, but we don't recommend this.

  • Uppercase and lowercase letters aren't distinct. For example, Smith and SMITH refer to the same variable.

  • The maximum length of a variable name is 128 characters.

  • A variable can't have the same name as an AL method or a reserved word. This applies to both uppercase and lowercase spellings. For example, you can't use begin as a valid variable name.

When you name a variable, you can't use special characters unless you enclose the variable name in quotation marks, as in "Customer No.". If you don't use double quotation marks, then the following rules apply:

  • The first character must be one of the following:
  • A letter or an underscore
  • The first character is followed by a maximum of 29 characters, which can be any of the following:
    • A letter
    • An underscore
    • A digit

You can include one or more special characters in a variable name in AL. If you do include special characters, then the variable name must be enclosed in quotation marks. In this case, the name can contain any mix of letters, digits, and special characters.

Note

The quotation marks aren't part of the variable name but are required to successfully compile the codeunit.

Examples

The following examples show valid variable names:

  • Customer
  • StockGroup1
  • "@Vendor"
  • "first AddressLine"
  • "Purchase/Sales"
  • "Sales in GBP"
  • "Name with Special Characters1Ñ3"

The following examples show incorrect variable names:

  • 34467
  • 23"Tubes
  • Stock Group4
  • "Sale"s in GBP"
  • )-Names
  • END

Initialization

Variables are automatically initialized before the AL code is run. A boolean variable is set to false. Numeric variables are set to the default value zero. Strings (text and code) are initialized to the value '' (an empty string). date and time variables are set to the undefined time 0T and the undefined date 0D, respectively. Variables of complex data types are also initialized. If a complex data type has multiple components, then each component is initialized to the value that corresponds to the data type for the component.

System-defined variables are automatically handled and initialized. No actions are required by the user before system-defined variables can be used.

Assignment and type conversion

You can assign values in the following ways:

  • By using the assignment operator :=, such as Variable := Expression. The data type that results from the evaluation of the right side expression must be the same data type as the variable (left operand) or have a data type that can be converted automatically to the data type of the left operand.

  • As parameter assignment, such as method(Expression). The data type that results from the evaluation of the expression must correspond to a specific data type or have a data type that can be converted automatically to the correct data type. For more information about evaluation and type conversion in expressions, see AL type conversion in expressions.

Automatic type conversion in assignments occurs when the following events occur:

  • A parameter in a method call doesn't have the correct data type. For example, this can occur if a method that's supposed to be called by using an integer argument is called by using a DateTime argument.

    Note

    If the value can't be converted, then a runtime error occurs. If the value can be converted but overflow occurs, then a runtime error occurs.

  • The evaluation of the expression on the right side of an assignment operator := achieves a data type that differs from the data type of the variable on the left side, and the expression can be converted to the data type of the variable.

Automatic type conversion in assignments can occur between the following numeric data types as long as an overflow doesn't occur:

  • Byte
  • Char
  • Integer
  • Decimal

Automatic type conversion in assignments can occur between the string data types:

  • Code
  • Text

The same assignment rules apply for arrays in AL. Furthermore, if the left operand in an assignment (the variable) is an array, the dimension or dimensions of the right side expression must correspond to the dimension or dimensions of the variable.

Note

The type conversion that occurs in assignments can cause runtime errors even though the data types are convertible. A runtime error can occur in an assignment if the converted value is outside the valid range for the left side variable. Also, a runtime error can occur if the converted value is outside the valid range for a parameter in a method call.

Valid assignments

The following tables show whether you can assign the value of an expression of a given type to a variable of the same type or to a variable of a different type.

This table shows the numeric data types.

Char expression Option expression Integer expression BigInteger expression Duration expression Decimal expression
Char variable Valid Valid but overflow might occur Valid but overflow might occur Valid but overflow might occur Valid but overflow might occur Valid but overflow might occur
Option variable Valid Valid Valid Valid but overflow might occur Valid but overflow might occur Valid but overflow might occur
Integer Valid Valid Valid Valid but overflow might occur Valid but overflow might occur Valid but overflow might occur
BigInteger variable Valid Valid Valid Valid Valid Valid but overflow might occur
Duration variable Valid Valid Valid Valid Valid Valid but overflow might occur
Decimal variable Valid Valid Valid Valid but overflow might occur Valid but overflow might occur Valid

This table shows the string data types.

Text expression Code expression
Text variable Valid but overflow might occur Valid but overflow might occur
Code variable Valid but overflow might occur Valid but overflow might occur

Note

You can assign a BigText variable using the BigText methods. For more information, see BigText Data Type.

System-defined variables
AL method reference
Properties