The CompositePrincipal signature is inconvenient to use

[mitchlloyd]

Describe the bug
The new CompositePrincipal() constructor accepts a list of PolicyPrinciples as arguments. I'd like to be able to refactor my code to pass an array of principals, but the type is fighting me.

const compositePrincipal = new iam.CompositePrincipal(...authorizedPrincipals);
// Type error: Expected at least 1 arguments, but got 0 or more.

I realize there is a tradeoff here, since logically we'd like to have at least 1 principal in a composite principal. However, I feel that the benefit of a type error for new iam.CompositePrincipal() (rather than a synth-time error) is less than the benefit of being able to pass an array as arguments.

To Reproduce

import * as iam from '@aws-cdk/aws-iam';

const ps = [new iam.AccountPrincipal('123'), new iam.AccountPrincipal('456')];
new iam.CompositePrincipal(...ps);

Expected behavior
No type errors.

Version:

• OS: OSX
• Programming Language: TypeScript
• CDK Version: 0.19.0 (build 2625a05) (but also current version)

[rix0rrr]

That is a fair point, and it's actually an instance of a design strategy I hate myself (designing APIs for direct human use only, to the neglect of higher-level abstractions).

I concur, it should be an array with a run-time check.

[rix0rrr]

Although it's honestly not that hard to work around:

new iam.CompositePrincipal(ps[0], ...ps.slice(1));

[mitchlloyd]

That's what I did ^, but making consumers jump through that hoop seems unfortunate.