Passing field to custom function as object rather than the field's value

[Quartekoen]

This is something I've been wondering about for a while.

It's obvious that there's a difference between how some FM functions work compared to others. For example, when you say ABS( some::field ), it returns the absolute value of the value of that field. However, when you use GetFieldName( some::field ), it doesn't use the value of the field, but rather the properties of the field itself. This is fantastically useful.

So is there any way that I can make a custom function that acts like GetFieldName? Let's say I want to write a simple function that extracts the database name of a field that I pass in. It would be great if I could just call the function like GetDBName( some::field ) and have it know that it needs to parse the field name property of the field rather than using the value in the field.

[Søren Dyhr]

Isn't it in the vicinity of the scope of this article?

http://sixfriedrice.com/wp/set-field-by-name-exposed/

[comment]

You are right that Filemaker is inconsistent in the way it distinguishes between a field value and a reference to the field itself. However, the parameters of a custom function will always be interpreted as values.

You still can send a field name (as a text string) to your function, and use GetField() to convert it to a reference. To protect against future changes in the field's name, call your function as =

MyCustomFunction ( GetFieldName ( MyField ) )

[Quartekoen]

Soren: Close, but not really. What I'm interested in is passing the field reference to a custom function rather than a script.

comment: Thanks. I figured as much, and what you suggested is what I've been using. I was just wondering if there's an easier way. Hopefully this will be added in a later version of FM! Also, I believe that GetField( myField ) doesn't convert it to a reference, but rather gets the contents of myField.

[comment]

I believe that GetField( myField ) doesn't convert it to a reference, but rather gets the contents of myField.

No, that's not quite accurate. GetField ( MyField ) converts the contents of MyField into a reference. GetField ( "MyField" ) converts the text string "MyField" into a reference to the MyField field - and a reference to a field is evaluated as the field contents.

[jbante]

However, the parameters of a custom function will always be interpreted as values.

This is incorrect. Consider this custom function, which takes a field (*not* a field name) as a parameter: https://github.com/f...meVariable.fmfn

// GetFieldNameVariable ( field ; prefix )

// Example use (in field auto-enter calculation): GetFieldNameVariable ( Self ; "$" )

Let ( [

var.field = GetFieldName ( field );

var.parts = Substitute ( var.field ; "::" ; ¶ );

var.result = Evaluate ( prefix & GetValue ( var.parts ; 2 ) )

];

If ( var.result = "?" ; False ; var.result )

)

The fact that the "GetFieldName ( field )" line works in this function suggests that a custom function argument is capable of acting as a reference. Getting back to what I assume Quartekoen was mentioning as a starting example, this custom function along the same lines also works:

// GetTableName ( field )

Let ( [

~name = GetFieldName ( field );

~values = Substitute ( ~name ; "::" ; ¶ )

];

GetValue ( ~values ; 1 )

)

[comment]

This is incorrect.

Yes, you are right. There are a few functions that will interpret a parameter as a field reference (that's what I meant by Filemaker being inconsistent).