Compact syntax for getting, setting header values and comments

[sefffal]

Hi all, Thanks for this package.

Here is an idea and implementation for a compact syntax for getting and setting header values and comments at the same time:

# Make a header to use in demo
header = FITSHeader(["key1"], [1], ["comment 1"])

# Get a value and comment using :
value, comment = header["key1", :]

# Set a new value and comment
header["key2",:] = 2.0, "the second comment"

This was done by overriding getindex and setindex! for the colon argument. If this is interesting, I would be happy to add tests etc.

Thanks for reading!

[kbarbary]

Cool. I think a compact syntax for this would be great. Colon seems a little weird, since I'd expect header["key", :] to return a 1-d array, in analogy with other data structures (like 2-d Arrays). I was wondering if using a special symbol value like header["key", :comment] would be more explicit?

[mileslucas]

Or perhaps something like header[“key”, !] if we want to really differentiate it from slice indexing (or any other small symbol function like ^, *, +, <, etc) without writing out “:comment”.

[emmt]

Why not passing a tuple (val, com) with the value and comment instead of just val when you just want to change the value? This is what I have done in EasyFITS.jl (an attempt to simplify dealing with FITS files).

[mileslucas]

I think that creates an asymmetry in design, because that would only work with `setindex!’, we still need a way to get the comment out using some compact notation

[emmt]

OK then back to the previous suggestion, why not with an additional / after the key as a reminder that this symbol is the value-comment separator in FITS header?

[sefffal]

Good points about the colon, it is a bit odd. I like the / suggestion since it looks like a FITS comment. Would we use it for directly accessing the comment (not a value and comment tuple)?

e.g.

header["KEY"] = 1
header["KEY", /] = "comment"