3.1 Introduction to Namespace

A namespace is a language element that combines other language elements into a combination. The name of a language element declared in one namespace can be used in other namespaces
Elements of the namespace can be accessed outside the namespace by adding the namespace name in front. Being in the same namespace is not required but allows access by this method

Namespace can avoid naming conflicts of identifiers such as variables and functions

For specific UI usage, please refer to User Manual
SYS is the system library namespace, which can be accessed by default users. SYS is referenced by default when compiling
Users need to write the namespace name when writing STRUCT, GVS, and PU
For PRG variables, the PRG name is a sub-namespace; the full access path is ".namespace.PRG name.Variable name". user can directly use the variable name to access within this PRG
For GVS variables, the full access path is ".namespace.variable name"
For the STRUCT type, the full access path is ".namespace.STRUCT name"
For FB type, the full access path is ".namespace.FB name"
Access to FB instance
- If the FB instance is declared in GVS, the full access path is ".namespace.FB instance name"
- If the FB instance is declared in another FB, the FB instance can only be accessed in the FB where the current FB instance variable is declared. Use the "FB instance name" directly
For FC calls, the full access path is ".namespace.FC name"
Referenced in the same namespace, the namespace can be defaulted, but if the related name exists in SYS in the default mode, compilation error will occur. The namespace cannot be defaulted at this time

Serial number	Object identifier	Modify only this object identifier	Reconstruct all referenced objects
1	Default namespace	Only modify the default namespace name and do not reconstruct other objects
2	GVS namespace name	Only modify the GVS namespace name	Rename this GVS namespace + reconstruct the references of all global variables under this GVS name (including: IO mapping table, monitoring table)
3	The namespace name of the PRG	Modify only the namespace name of the PRG and change it to the file name simultaneously	Rename the namespace of this PRG + reconstruct all references to this PRG, including references to all variables of the PRG; including monitoring tables
4	FC namespace name	Modify only the FC namespace name and modify the file name simultaneously	Rename this FC namespace + reconstruct all references (calls) of this FC
5	FB namespace name	Modify only the FB namespace name and modify the file name simultaneously	Rename this FB namespace + reconstruct the FB type in all instance declarations of this FB
6	Namespace name of UDT (struct)	Modify only the namespace name of the STRUCT and modify the file name simultaneously	Rename this UDT namespace + reconstruct the UDT type in all instance declarations of this UDT

warning

"." represents the global namespace. The global namespace "." can only be followed by a specific first-level namespace name, not other object identifiers (variable names, PU names, UDT names). In other words, variable names, PU names, and UDT names must be defined with specific namespace names
Users cannot use "SYS" as the first-level namespace name. "SYS" is the first-level namespace name of the system library, and user program units can access it by default. When the system is compiled, "SYS" will be referenced by default ("SYS" is only the first-level namespace name occupied by the system, not a keywords)
In the same namespace, member names cannot be repeated
Variable names, PU names, and UDT names must start with "." if they use full access paths. However, if the namespace of a global variable is a sub-namespace of a PU namespace, the global variable can be accessed in the PU using "sub-namespace.variable name"
When the identifier is accessed using a fully qualified name, it must start with "."
If the object name in the program unit does not start with ".", the system will only check the current namespace of the PU and members under SYS (including sub-namespaces) by default
When compiling, the variables in the program unit that do not start with "." are queried from local to global. If both local and global variables exist, local variables are accessed first