| Navigation: Language Reference > 3 - Variable Declarations > Special Data Types >====== LIKE (inherited data type) ====== |    |
new declaration LIKE(like declaration) [,DIM( )] [,OVER( )] [,PRE( )] [,NAME( )] [,EXTERNAL]
[,DLL][,STATIC] [,THREAD] [,BINDABLE]
| LIKE | Declares a variable whose data type is inherited from another variable. |
| new declaration | The label of the new data element declaration. |
| like declaration | The label of the data element declaration whose definition will be used. This may be any simple data type, or a reference to any simple data type (except &STRING), or the label of a GROUP or QUEUE structure. |
| DIM | Dimension the variables into an array. |
| OVER | Share a memory location with another variable or structure. |
| PRE | Declare a label prefix for variables within the new declaration structure (if the like declaration is a complex data structure). This is not required, since you may use the new declaration in the Field Qualification syntax to directly reference any member of the new structure. |
| NAME | Specify an alternate, “external” name for the field. |
| EXTERNAL | Specify the variable is defined, and its memory is allocated, in an external library. Not valid within FILE, QUEUE, or GROUP declarations. |
| DLL | Specify the variable is defined in a .DLL. This is required in addition to the EXTERNAL attribute. |
| STATIC | Specify the variable's memory is permanently allocated. |
| THREAD | Specify memory for the variable is allocated once for each execution thread. Also implicitly adds the STATIC attribute on Procedure Local data. |
| BINDABLE | Specify all variables in the group may be used in dynamic expressions. |
LIKE tells the compiler to define the new declaration using the same definition as the like declaration, including all attributes. If the original like declaration changes, so does the new declaration.
The new declaration may use the DIM and OVER attributes. If the like declaration has a DIM attribute, the new declaration is already an array. If a further DIM attribute is added to the new declaration, the array is further dimensioned.
The PRE and NAME attributes may be used, if appropriate. If the like declaration already has these attributes, the new declaration will inherit them and compiler errors can occur. To correct this, specify a PRE or NAME attribute on the new declaration to override the inherited attribute.
If the like declaration names a QUEUE, LIKE does not create a new QUEUE, because the like declaration is simply treated as a GROUP. The like declaration QUEUE is converted to a new declaration GROUP. The same is true if the like declaration is a RECORD structure. Similarly, if the like declaration is a MEMO, the new declaration becomes a STRING of the maximum size of the MEMO.
You may use LIKE to create a new instance of a CLASS. However, simply declaring the new instance by naming the CLASS as the data type performs an implicit LIKE. For either type of instance declaration, the DIM, OVER, PRE, and NAME attributes are invalid; all other attributes are valid for a CLASS instance declaration.
Example:
Amount REAL !Define a field
QTDAmount LIKE(Amount) !Use same definition
YTDAmount LIKE(QTDAmount) !Use same definition again
MonthlyAmts LIKE(Amount),DIM(12) !Use same definition for array, 12 elements
AmtPrPerson LIKE(MonthlyAmts),DIM(10)
!Use same definition for array of 120 elements (12,10)
Construct GROUP !Define a group
Field1 LIKE(Amount) ! Construct.field1 - real
Field2 STRING(10) ! Construct.field2 - string(10)
END
NewGroup LIKE(Construct) !Define new group, containing
! NewGroup.field1 - real
! NewGroup.field2 - string(10)
MyQue QUEUE !Define a queue
Field1 STRING(10)
Field2 STRING(10)
END
MyGroup LIKE(MyQue) !Define new GROUP, like the QUEUE
AmountFile FILE,DRIVER('Clarion'),PRE(Amt)
Record RECORD
Amount REAL !Define a field
QTDAmount LIKE(Amount) !Use same definition
END
END
Animal CLASS
Feed PROCEDURE(short amount),VIRTUAL
Die PROCEDURE
Age LONG
Weight LONG
END
Cat LIKE(Animal) !New instance of an Animal CLASS
Bird Animal !New instance of an Animal CLASS (implicit LIKE)
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