set order of attributes

[JHenneberg]

While reading the style guide STYLE_GUIDE.md I noticed that the order of the attributes is not specified.

Going through the source files the order seems:

1. allocatable
2. dimension
3. intent(intent-spec)
4. optional

Although it is not clear if allocatable should be after oder before dimension

Missing attributes I can think of right now are:

• target, pointer
• parameter
• public, private, protected
• asynchronous
• save
• external
• contiguous
• volatile

So lets come up with a convention for the order of attributes.

Suggestion so far for STYLE_GUIDE.md

# Order of attributes

Similiar to the guidlines for indentation and whitespace, specifiying the order of appearance of attributes can  help reviewing code and git-diffs.

1. ```allocatable```
2. ```dimension```
3. ```intent(<>)```
4. ...

[jvdp1]

Good point.
I usually write things in this order:

1. dimension
2. allocatable
3. intent(intent-spec)
4. optional

Some combinations of attributes are not possible.
Could you maybe submit a PR with suggested modifications for further discussions?

[certik]

I do not follow a strict order, although typically intent() is at the end, the allocatable and dimension I use in any order, and optional is typically around intent() in either order.

Is it important to always follow a certain order? It seems maybe we do not need to standardize this?

[milancurcic]

I tend to write these attributes in the same order as @jvdp1. More lately, I prefer to omit dimension, so:

real, dimension(:), allocatable :: a
real, dimension(:,:), allocatable :: b

becomes just:

real, allocatable :: a(:), b(:,:)

Not only is the code less verbose by not including dimension, but also arrays of different size, shape, or rank can be declared on the same line.

Like @certik, I don't think the order is as important. Rather than enforcing the order, I'd prefer seeing these two clauses:

• Don't use dimension attribute to declare arrays
• Always specify intent for dummy arguments

If we did indeed specify order of attributes in the style guide, I'd personally like to see:

• intent attribute should be specified last in the declaration statement
• If optional attribute is used to declare a dummy argument, it should follow the intent attribute

or similar.

[certik]

I agree with @milancurcic. I also prefer not to use dimension, the only exception is if I have a lot of arrays of the same dimension (of high rank), such as here:

https://github.com/certik/hfsolver/blob/b4c50c1979fb7e468b1852b144ba756f5a51788d/src/ofdft_fe.f90#L249

then it saves lots of typing.