[J3] Why is += missing?

[Jeff Hammond]

I will argue that it is syntactic sugar in the same sense that multidimensional arrays are.  Below is the perfectly functional C code I wrote to match my Fortran years ago (because computer scientists don’t know their history).  There is no actual need for multidimensional arrays in Fortran, just the practical difficulty of not having them.

// t3(h3,h2,h1,p6,p5,p4)+=t1(p4,h1)*v2(h3,h2,p6,p5);
t3[h3+h3u*(h2+h2u*(h1+h1u*(p6+p6u*(p5+p5u*p4))))] += t1[p4+p4u*h1] * v2[h3+h3u*(h2+h2u*(p6+p6u*p5))];

I think the relative usage of +=, -=, *=, ÷=, and **= if they were added justifies the pragmatic solution of just doing += and -=, which are more likely to have hardware support anyways.

Jeff

From: J3 <j3-bounces at mailman.j3-fortran.org> on behalf of Steve Lionel via J3 <j3 at mailman.j3-fortran.org>
Date: Wednesday, August 25, 2021 at 4:13 PM
To: j3 at mailman.j3-fortran.org <j3 at mailman.j3-fortran.org>
Cc: Steve Lionel <steve at stevelionel.com>
Subject: Re: [J3] Why is += missing?
External email: Use caution opening links or attachments

On 8/25/2021 8:07 AM, Jeff Hammond via J3 wrote:
After 15 years as a Fortran programmer, I am still annoyed on a daily basis about the tedium imposed on me because Fortran lacks +=.
This was considered - there were a few requests for it in the 202X survey we ran 2017-2018. I suspect it fell off the list because of 1)  it is "syntactic sugar", not adding any new capability and 2) the existing use of /= requiring some complicated exceptions. It could be done, sure, but the demand seems low. We'll soon start the process for 202Y features - feel free to put it forward then.

Steve
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