Template: field vs raw_field

[ownedbycats]

I have an integer column with formatting {0}%

Which of these is better practice?

program:
	if field('#percentread') == '0%' then '1'
	fi

program:
	if raw_field('#percentread') ==# '0' then '1'
	fi

I know the differences between lexical and numerical but this is exact match so i am not sure if there is any difference. I am using the second currently.

[chaley]

Originally Posted by ownedbycats

Which of these is better practice?

It depends.

The underlying problem is the same as you solve with check_yes_no(), what to do with undefined values. What do you want to happen in this case? Is 'undefined' the same as '0'? Is it something else? If defined, what comparisons are needed?

For integers the field() function returns the empty string if the book's value is not defined, otherwise (as you said) the formatted value. If undefined is to be treated as zero and you aren't doing any non-equal comparisons then you need

v = field('#percentread');
if !v || v == '0%' then

With raw_field() you have the choice of what is returned for undefined values. For example:

• x is undefined: raw_field(x) returns 'none'
• x is undefined: raw_field(x, 0) returns 0 (zero)
• x is undefined: raw_field(x, -1000) returns -1000
• x is undefined: raw_field(x, '') returns the empty string
• x is undefined: raw_field(x, 'twas brillig') returns the string 'twas brillig'
• x is defined: all the above raw_field() examples return x unformatted.

In the end, what you do is a matter of personal preference. You must understand what the code does for the possible range of values. You must be able to maintain it, which means understanding the code again in the future.

My preference is to use raw_field, setting the default to what makes sense in the context. That isolates me from the vagaries of formatting (which can change) and lets me use non-identical comparisons without thinking too much about it. If we assume that undefined values are to be treated as zero then this:

v = raw_field('lookup key', 0)
if v ==# 0 then

If later I look at this code then it is easy for me to know that the field is numeric and undefined values are assumed to be zero. It will work if later I decide that I want decimal percentages, e.g., 43.5% or 0.0%.

And yes, I know I get rather pedantic.

[ownedbycats]

On this topic:

program:
	if raw_field('#percentread') ==# '0' then '1'
	else raw_field('#percentread')
	fi

Running this on a book with #percentread undefined returns result as 1.What is the proper way to make it remain undefined?

I changed it to raw_field('#percentread', '1') and it remained undefined but that felt kludge. Empty string '' returned a 1 not sure why.

[chaley]

Originally Posted by ownedbycats

On this topic:

program:
	if raw_field('#percentread') ==# '0' then '1'
	else raw_field('#percentread')
	fi

Running this on a book with #percentread undefined returns result as 1.What is the proper way to make it remain undefined?

I changed it to raw_field('#percentread', '1') and it remained undefined but that felt kludge. Empty string '' returned a 1 not sure why.

Here is what I would do.

program:
	v = raw_field('#myint', '');
	if !v then
		''
	elif v ==# 0 then
		'1'
	else
		 v
	fi

This is the same thing but not using the second parameter of raw_field.

program:
	v = raw_field('#myint');
	if v == 'none' then
		''
	elif v ==# 0 then
		'1'
	else
		 v
	fi

[ownedbycats]

That works. What exactly does the !v do?

[chaley]

Originally Posted by ownedbycats

That works. What exactly does the !v do?

The ! (bang) is the logical 'not' operator. "Bang v" returns True ('1') if v is False (''), or False ('') if v is True (anything but '').