How to know whether parameter expects an expression? Topic is solved

[Avtem]

Take for example StringReplace function. How should I know that OutputVar (first parameter) should be an expression? There is no such thing in the documentation that says: "this parameter must be an expression" or "this parameter must use legacy syntax".
Does user have to guess/deduce/try whether treat parameter as expression/legacy syntax?

[mikeyww]

That command is deprecated, but an output variable is simply a variable name and nothing more or less. Fortunately, all of the commands come with examples in the documentation.

OutputVar. The name of the variable in which to store the result of the replacement process.

[gregster]

In short:
Outputvar parameters: never expressions (but variable names)
all other parameters: just force expression mode (% with a space following) for them, if you are unsure.

Details:

Spoiler

Usually commands require "legacy" syntax, unless the docs give you other options, eg Sleep's delay parameter:

Delay

The amount of time to pause (in milliseconds) between 0 and 2147483647 (24 days), which can be an expression.

As a rule of thumb: a (non-output) parameter can usually be natively an expression, if the parameter is purely numeric (but the docs will tell you).


Output variable parameters are never expressions, for example:

OutputVarX, OutputVarY

The names of the variables in which to store the X and Y coordinates of the upper-left pixel of where the image [...]

Of course, you can also force expressions instead of using legacy syntax (except for outputvar paramters):

Force an expression: An expression can be used in a parameter that does not directly support it (except OutputVar parameters) by preceding the expression with a percent sign and a space or tab. In [v1.1.21+], this prefix can be used in the InputVar parameters of all commands except the traditional IF commands (use If (expression) instead).

So...

Take for example StringReplace function. How should I know that OutputVar (first parameter) should be an expression?

Well, it shouldn't be an expression. Command outputvar parameters are never expressions (see above).

If, on the other hand, an input parameter can be an expression, the docs will tell you (but these will be purely numeric parameters, like delays or coordinates).
For all (other) input (non-output) paras, you can always force an expression (incl. the purely numeric ones, but for them it will be redundant).


PS:
This might help: https://www.autohotkey.com/docs/Language.htm#commands (and following sections)

Some users may find it easier to always force an expression, keeping to one consistent syntax (expression syntax) as much as possible.

(Again, this is for any non-outputvar parameters.)

[Avtem]

@gregster Thank you so much, gregster for your detailed answer. So now i can see why it was confusing to me, because i use commands with "output var name" parameters very often.

So i want to learn how to use everything, because not everyone always forces an expression, right? And i want to be able to understand the other's people code.

But now i think i understand pretty much everything about this topic, so this topic can be closed now.

[boiler]

So i want to learn how to use everything, because not everyone always forces an expression, right? And i want to be able to understand the other's people code.

The times you see an expression in a command parameter without forcing an expression are when the documentation states that a particular parameter “can be an expression.” See the documentation for Sleep, for example. That allows for the following without a forced expression:

Code: Select all

Sleep, Minutes * 60 * 1000