perf(core): optimize reflector

[zanminkian]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[jmcdo29]

Why this instead of the this.getAll()? Just for an early stop if a value is found?

[jmcdo29]

If you're going to refactor this to a raw for loop, we should do the same to the getAll for squeezing as much performance out as we can.

Side note: do you have any benchmarks for how much of an improvement this is? Just curious if the improvement is going to be worth the readability

[zanminkian]

I think raw for loop is not the mainly reason. Just break the loop earlier to increase the performance.

[zanminkian]

Seems not increase too much. This is a choice between a little performance and readability. :P

function get(num) {
    for(let i = 0; i < 100; i++) {
        num++
    }
    return num
}

function test1() {
    const start = process.hrtime.bigint();
    for(let i = 0; i< 10000; i++) {
        const targets = [100, 1000, 10000]
        targets.map(target=>get(target)).find(item => item !== undefined)
    }
    console.log(process.hrtime.bigint()-start);
}

function test2() {
    const start = process.hrtime.bigint();
    for(let i = 0; i< 10000; i++) {
        const targets = [100, 1000, 10000]
        for(const target of targets) {
            const res = get(target)
            if(res !== undefined) {
                break;
            }
        }
    }
    console.log(process.hrtime.bigint()-start);
}

function test3() {
    const start = process.hrtime.bigint();
    for(let i = 0; i< 10000; i++) {
        const targets = [100, 1000, 10000]
        for(const target of targets) {
            const res = get(target)
            if(res !== undefined) {
                // break;
            }
        }
    }
    console.log(process.hrtime.bigint()-start);
}

test1() // 119022900n
test2() // 4902500n
test3() // 7564600n

[coveralls]

Pull Request Test Coverage Report for Build f3608146-d290-4a7e-a1ce-5fbbf02b5f37

• 6 of 7 (85.71%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 93.813%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/core/services/reflector.service.ts	6	7	85.71%

Files with Coverage Reduction	New Missed Lines	%
packages/core/repl/repl-context.ts	1	85.54%

Totals
Change from base Build 7429007a-3efb-492d-a2a1-84f706a41b5f:	-0.01%
Covered Lines:	6096
Relevant Lines:	6498

---

💛 - Coveralls

[kamilmysliwiec]

lgtm