Some preprocessing capabilities are included in PlantUML, and available for all diagrams. Those functionalities are very similar to the C language preprocessor, except that the special character # has been changed to the exclamation mark !.
Variable definition [=, ?=]
Although this is not mandatory, we highly suggest that variable names start with a $. There are three types of data:
Integer number(int);
String(str) - these must be surrounded by single quote or double quote;
JSON(JSON) - these must be surrounded by curly brackets.
(for JSON variable definition and usage, see more details on Preprocessing-JSON page) Variables created outside function are global, that is you can access them from everywhere (including from functions). You can emphasize this by using the optional global keyword when defining a variable.
@startuml
!$a = 42
!$ab = "foo1"
!$cd = "foo2"
!$ef = $ab + $cd
!$foo = { "name": "John", "age" : 30 }
Alice -> Bob : $a
Alice -> Bob : $ab
Alice -> Bob : $cd
Alice -> Bob : $ef
Alice -> Bob : Do you know **$foo.name** ?
@enduml
You can also assign a value to a variable, only if it is not already defined, with the syntax: !$a ?= "foo"
@startuml
Alice -> Bob : 1. **$name** should be empty
!$name ?= "Charlie"
Alice -> Bob : 2. **$name** should be Charlie
!$name = "David"
Alice -> Bob : 3. **$name** should be David
!$name ?= "Ethan"
Alice -> Bob : 4. **$name** should be David
@enduml
Boolean expression
Boolean representation [0 is false]
There is not real boolean type, but PlantUML use this integer convention:
Integer 0 means false
and any non-null number (as 1) or any string (as "1", or even "0") means true.
@startuml
!$a = 10
!$ijk = "foo"
Alice -> Bob : A
!if ($ijk == "foo") && ($a+10>=4)
Alice -> Bob : yes
!else
Alice -> Bob : This should not appear
!endif
Alice -> Bob : B
@enduml
While loop [!while, !endwhile]
You can use !while and !endwhile keywords to have repeat loops.
Variables defined in procedures are local. It means that the variable is destroyed when the procedure ends.
Return function [!function, !endfunction]
A return function does not output any text. It just define a function that you can call:
directly in variable definition or in diagram text
from other return functions
from procedures
Function name should start with a $
Argument names should start with a $
@startuml
!function $double($a)
!return $a + $a
!endfunction
Alice -> Bob : The double of 3 is $double(3)
@enduml
It is possible to shorten simple function definition in one line:
@startuml
!function $double($a) !return $a + $a
Alice -> Bob : The double of 3 is $double(3)
Alice -> Bob : $double("This work also for strings.")
@enduml
As in procedure (void function), variable are local by default (they are destroyed when the function is exited). However, you can access to global variables from function. However, you can use the local keyword to create a local variable if ever a global variable exists with the same name.
@startuml
!function $dummy()
!local $ijk = "local"
!return "Alice -> Bob : " + $ijk
!endfunction
!global $ijk = "foo"
Alice -> Bob : $ijk
$dummy()
Alice -> Bob : $ijk
@enduml
Default argument value
In both procedure and return functions, you can define default values for arguments.
@startuml
!function $inc($value, $step=1)
!return $value + $step
!endfunction
Alice -> Bob : Just one more $inc(3)
Alice -> Bob : Add two to three : $inc(3, 2)
@enduml
Only arguments at the end of the parameter list can have default values.
@startuml
!procedure defaulttest($x, $y="DefaultY", $z="DefaultZ")
note over Alice
x = $x
y = $y
z = $z
end note
!endprocedure
defaulttest(1, 2, 3)
defaulttest(1, 2)
defaulttest(1)
@enduml
Unquoted procedure or function [!unquoted]
By default, you have to put quotes when you call a function or a procedure. It is possible to use the unquoted keyword to indicate that a function or a procedure does not require quotes for its arguments.
@startuml
!unquoted function id($text1, $text2="FOO") !return $text1 + $text2
alice -> bob : id(aa)
alice -> bob : id(ab,cd)
@enduml
Keywords arguments
Like in Python, you can use keywords arguments :
@startuml
!unquoted procedure $element($alias, $description="", $label="", $technology="", $size=12, $colour="green")
rectangle $alias as "
<color:$colour><<$alias>></color>
==$label==
//<size:$size>[$technology]</size>//
$description"
!endprocedure
$element(myalias, "This description is %newline()on several lines", $size=10, $technology="Java")
@enduml
Including files or URL [!include, !include_many, !include_once]
Use the !include directive to include file in your diagram. Using URL, you can also include file from Internet/Intranet. Imagine you have the very same class that appears in many diagrams. Instead of duplicating the description of this class, you can define a file that contains the description.
@startuml
interface List
List : int size()
List : void clear()
List <|.. ArrayList
@enduml
File List.iuml
interface List
List : int size()
List : void clear()
The file List.iuml can be included in many diagrams, and any modification in this file will change all diagrams that include it. You can also put several @startuml/@enduml text block in an included file and then specify which block you want to include adding !0 where 0 is the block number. The !0 notation denotes the first diagram. For example, if you use !include foo.txt!1, the second @startuml/@enduml block within foo.txt will be included. You can also put an id to some @startuml/@enduml text block in an included file using @startuml(id=MY_OWN_ID) syntax and then include the block adding !MY_OWN_ID when including the file, so using something like !include foo.txt!MY_OWN_ID. By default, a file can only be included once. You can use !include_many instead of !include if you want to include some file several times. Note that there is also a !include_once directive that raises an error if a file is included several times.
Including Subpart [!startsub, !endsub, !includesub]
You can also use !startsub NAME and !endsub to indicate sections of text to include from other files using !includesub. For example: file1.puml:
@startuml
A -> A : stuff1
!startsub BASIC
B -> B : stuff2
!endsub
C -> C : stuff3
!startsub BASIC
D -> D : stuff4
!endsub
@enduml
file1.puml would be rendered exactly as if it were:
@startuml
A -> A : stuff1
B -> B : stuff2
C -> C : stuff3
D -> D : stuff4
@enduml
However, this would also allow you to have another file2.puml like this: file2.puml
@startuml
title this contains only B and D
!includesub file1.puml!BASIC
@enduml
This file would be rendered exactly as if:
@startuml
title this contains only B and D
B -> B : stuff2
D -> D : stuff4
@enduml
Builtin functions [%]
Some functions are defined by default. Their name starts by %
Name
Description
Example
Return
%darken
Return a darken color of a given color with some ratio
You can use !log to add some log output when generating the diagram. This has no impact at all on the diagram itself. However, those logs are printed in the command line's output stream. This could be useful for debug purpose.
@startuml
!function bold($text)
!$result = "<b>"+ $text +"</b>"
!log Calling bold function with $text. The result is $result
!return $result
!endfunction
Alice -> Bob : This is bold("bold")
Alice -> Bob : This is bold("a second call")
@enduml
Memory dump [!memory_dump]
You can use !memory_dump to dump the full content of the memory when generating the diagram. An optional string can be put after !memory_dump. This has no impact at all on the diagram itself. This could be useful for debug purpose.
@startuml
!function $inc($string)
!$val = %intval($string)
!log value is $val
!dump_memory
!return $val+1
!endfunction
Alice -> Bob : 4 $inc("3")
!unused = "foo"
!dump_memory EOF
@enduml
Assertion [!assert]
You can put assertions in your diagram.
@startuml
Alice -> Bob : Hello
!assert %strpos("abcdef", "cd")==3 : "This always fails"
@enduml
Building custom library [!import, !include]
It's possible to package a set of included files into a single .zip or .jar archive. This single zip/jar can then be imported into your diagram using !import directive. Once the library has been imported, you can !include file from this single zip/jar. Example:
@startuml
!import /path/to/customLibrary.zip
' This just adds "customLibrary.zip" in the search path
!include myFolder/myFile.iuml
' Assuming that myFolder/myFile.iuml is located somewhere
' either inside "customLibrary.zip" or on the local filesystem
...
Search path
You can specify the java property plantuml.include.path in the command line. For example:
Note the this -D option has to put before the -jar option. -D options after the -jar option will be used to define constants within plantuml preprocessor.
Argument concatenation [##]
It is possible to append text to a macro argument using the ## syntax.
You can dynamically invoke a procedure using the special %invoke_procedure() procedure. This procedure takes as first argument the name of the actual procedure to be called. The optional following arguments are copied to the called procedure. For example, you can have:
@startuml
!procedure $go()
Bob -> Alice : hello
!endprocedure
!$wrapper = "$go"
%invoke_procedure($wrapper)
@enduml
@startuml
!procedure $go($txt)
Bob -> Alice : $txt
!endprocedure
%invoke_procedure("$go", "hello from Bob...")
@enduml
For return functions, you can use the corresponding special function %call_user_func() :
@startuml
!function bold($text)
!return "<b>"+ $text +"</b>"
!endfunction
Alice -> Bob : %call_user_func("bold", "Hello") there
@enduml
Evaluation of addition depending of data types [+]
Evaluation of $a + $b depending of type of $a or $b
@startuml
title
<#LightBlue>|= |= $a |= $b |= <U+0025>string($a + $b)|
<#LightGray>| type | str | str | str (concatenation) |
| example |= "a" |= "b" |= %string("a" + "b") |
<#LightGray>| type | str | int | str (concatenation) |
| ex.|= "a" |= 2 |= %string("a" + 2) |
<#LightGray>| type | str | int | str (concatenation) |
| ex.|= 1 |= "b" |= %string(1 + "b") |
<#LightGray>| type | bool | str | str (concatenation) |
| ex.|= <U+0025>true() |= "b" |= %string(%true() + "b") |
<#LightGray>| type | str | bool | str (concatenation) |
| ex.|= "a" |= <U+0025>false() |= %string("a" + %false()) |
<#LightGray>| type | int | int | int (addition of int) |
| ex.|= 1 |= 2 |= %string(1 + 2) |
<#LightGray>| type | bool | int | int (addition) |
| ex.|= <U+0025>true() |= 2 |= %string(%true() + 2) |
<#LightGray>| type | int | bool | int (addition) |
| ex.|= 1 |= <U+0025>false() |= %string(1 + %false()) |
<#LightGray>| type | int | int | int (addition) |
| ex.|= 1 |= <U+0025>intval("2") |= %string(1 + %intval("2")) |
end title
@enduml
Preprocessing JSON
You can extend the functionality of the current Preprocessing with JSON Preprocessing features:
The current preprocessor is an update from some legacy preprocessor. Even if some legacy features are still supported with the actual preprocessor, you should not use them any more (they might be removed in some long term future).
You should not use !define and !definelong anymore. Use !function, !procedure or variable definition instead.
!define should be replaced by return !function
!definelong should be replaced by !procedure.
!include now allows multiple inclusions : you don't have to use !include_many anymore
!include now accepts a URL, so you don't need !includeurl
Some features (like %date%) have been replaced by builtin functions (for example %date())
When calling a legacy !definelong macro with no arguments, you do have to use parenthesis. You have to use my_own_definelong() because my_own_definelong without parenthesis is not recognized by the new preprocessor.
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