Why I like Fortran (reason # 324)

[brooksmoses]

Consider the following simplified piece of a program that I was recently writing:

type vector
  real :: x, y, z
end type

type field
  type(vector) :: data(5,5,5)
end type

type(field) my_field

my_field%data(:,:,2)%z = 3

Most of that's just setup of user-defined variable types, and is nothing different than one would do in C++. It sets up a type called vector with real-number variables x, y, and z; sets up a field type containing a component data, which is a three-dimensional array of vectors (I've used fixed values for the dimensions to make things simple); and defines a variable my_field of this type. Also, Fortran has a slightly different notation for accessing components; one writes my_field%data rather than the my_field.data that most other languages use.

The part that's particularly nice about Fortran is the last line, which illustrates what I can do with this -- and, in particular, how array indexing works in combination with data structures of this sort. The index notation (:,:,2) represents the portion of the array where the first two indices can take on any value, but the third index is limited to 2 -- that is, a two-dimensional slice through the overall array. Thus, my_field%data(:,:,2)%z is exactly what it looks like -- a reference to all of the z components of the vectors that make up that slice. Fortran treats this as equivalent to any other two-dimensional array; in this case, I've assigned it to a constant value of 3, which simply sets the z components of all the elements in the slice to 3. That's a rather trivial example; there are far more interesting ones, like passing it as an argument to a function that expects a two-dimensional array of real numbers.

Comments

[necturus.livejournal.com]

That sure doesn't look like the Fortran I remember, where God was real unless declared integer, and statements had to be all in upper case and start in column 7. Hell, it didn't even have strings, let alone user-defined data types.

[brooksmoses]

Heh. Yup, the language has had a lot added to it with the Fortran-77 and Fortran-95 standards. (The strings and possibly the permission for compilers to support lower-case letters are in Fortran-77; the rest is in Fortran-95. And in Fortran-90, though there were only one or two Fortran-90 compilers written before the Fortran-95 standard came out.) With the Fortran-2003 standard, they've even added object-oriented capabilities.

It's still backwards compatible in the sense that a Fortran-95 compiler will correctly compile nearly any Fortran program from the Fortran you remember, though. And God is still real unless declared integer or otherwise.

[bungo.livejournal.com]

It ain't ya father's Fortran, any more.

(wave)

[tenacious-snail.livejournal.com]

Hi there

I don't think we've ever met IRL, but I just happened to check my snail mail, and discover something addressed to you sitting on top of the mailbox. Are you, indeed, my neighbor?

Les in 112

Re: (wave)

[brooksmoses]

Actually, I don't live here any more; we moved around to another complex at the other end of the block back in April.

However, I was just now visiting leback (who does live here) when the notification for your comment showed up in my inbox, and my new complex doesn't have a 112, so I walked over to the old mailbox -- where, indeed, there was some tax info that I needed (and had figured that I was going to have to put some effort into tracking down, because I remembered I'd forgotten to give them my new address) sitting on top of the mailbox. So thank you muchly for noticing it and commenting!

This is terribly, terribly amusing. (And we're certainly still close enough to count as neighbors, I think.)

Re: (wave)

[tenacious-snail.livejournal.com]

glad I could help! What amusing serendipity.