Object PmList (List of values)

Object represents a list of values.
Properties and methods:
GetCount Returns the number of values present in the list
AddHead Adds value to the beginning of the list
AddTail Adds value to the end of the list
GetHead Returns value from the beginning of the list
GetTail Returns value from the end of the list
RemoveHead Removes value from the beginning of the list
RemoveTail Removes value from the end of the list
SaveToArray Returns one-dimensional file of values queue
- The object can be created by the method Pm.CreatePmList.
- This object is functional also for Web panels. It is not functional in InternetExplorer8 and lower.
Values in this object form a list and can be accessed either from beginning (Head) or from the end (Tail) of the list. The values of the list can be:
- added: AddHead, AddTail
- read: GetHead, GetTail

Comparison of objects used for data storage:

The following object types can be used for holding values (of any data type). Each of these objects has certain advantages and disadvantages and the choice depends on the desired usage.

PmArray: This object contains values that are accessible by index in the array - it is possible to read any value at any time in this object. Reading and setting values is very fast, but adding is slow.

This object is functional only for JavaScript language. For the VBScript language the array is represented by Array data type.

PmList: This object contains a list of values. The values can be accessed only from the beginning or from the end of the list. Reading, adding amd removing values from beginning or end of the list is fast, but values "inside" the list cannot be accessed.

The object is designed for processing data as in "container" (stack, LIFO) or "queue" (pipe, FIFO).

PmMap: This object contains values that are addressed by name (text identifier). Value names represent object properties. The advanatege is the "clarity" of usage in the script code. The disadvantage is the inability to access the values in cycle by index.
PROMOTIC 8.3.30 SCADA system documentation - MICROSYS, spol. s r.o.

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