stan-dev / stan-dev/math

Add "array[] int, int" signature to infix operators + and -

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feature good first issue
Dominant language
C++
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Description

Description

When I try to add an array of integers and a single integer, I get the error:

Ill-typed arguments supplied to infix operator +. Available signatures: 
...
Instead supplied arguments of incompatible type: array[] int, int.

Is there a specific reason we don't have an array[] int, int signature for + and -?

Example

The following Stan code snippet will results in an error, but would be a well defined (vectorized) opteration I believe.

data {
  int N;
  array[N] int J;
}
transformed data {
  array[N] int K = J + N;
}

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the transformed-data Stan example with array[N] int J, J + N, and the corresponding - operation, then trace how Stan resolves infix operator signatures. Done means both operators accept array[] int, int and the example compiles without the reported type error.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
backend
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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