Macros: Why do middle default parameters not apply?

Question

 

Is this a bug? I define a macro: myMacro() with 3 parameters: myMacro(p1, p2="def2", p3="def3"), the last 2 parameters having default values. When I call the macro like this: myMacro("a1",,"a3") there is no way to only provide arguments for parameter 1 and 3. p2 will not use its default value.

See this more elaborate example:

---

@startuml

skinparam noteFontSize 20

!define showIcon(iconName, iconColor="#Purple", iconSize="12") <size:iconSize><color:iconColor><iconName></color></size>

note as N1
<back:#LightGreen>//OK, uses default values for iconColor and iconSize://</back>
""Follow this showIcon("&external-link") Link.""

<back:#LightGreen>//OK, uses default value for iconSize://</back>
""Change to showIcon("&fork", "#OrangeRed")Branch //master//.""

<back:#Red>//Not OK, does not use default value for iconColor://</back>
""Modify showIcon("&wrench",,"20") Settings.""

end note

@enduml

---

 

Answer 1

It's more a conception issue than a real bug.
As you have stated, there is indeed no way to only provide arguments for parameter 1 and 3 only.
You can either:

• provide only argument 1
• provide only arguments 1 and 2
• provide arguments 1, 2 and 3

As workaround, you have to define a second macro:
!define showIconPurple(iconName, iconSize="12") <size:iconSize><color:#Purple><iconName></color></size>

Is this a big issue for you ?

Comments

Thanks for the response. Well, it is not a big issue, just a bit counterintutive if the default character of parameters depends on their positional placement and if default values will only take effect if no arguments are provided for any consecutive parameters.

---

I may be wrong, but I think we have followed general rules used for example by C++ or PHP
https://en.wikipedia.org/wiki/Default_argument
http://stackoverflow.com/questions/10597114/php-default-function-parameter-values-how-to-pass-default-value-for-not-last