Generic is "any-like" for relational operators

[Rudxain]

🔎 Search Terms

generics templates comparison compare less-than more-than unknown unsound function inline

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about relational operators and comparisons

⏯ Playground Link

https://www.typescriptlang.org/play/?noUncheckedIndexedAccess=true&noUnusedLocals=true&noUnusedParameters=true&target=10&jsx=0&useUnknownInCatchVariables=true&exactOptionalPropertyTypes=true&noFallthroughCasesInSwitch=true&noImplicitOverride=true&noPropertyAccessFromIndexSignature=true&suppressImplicitAnyIndexErrors=true&ts=5.6.0-dev.20240619&noStrictGenericChecks=true#code/MYewdgzgLgBMC2AHGBeGAeAKgGgHwAoAPALhhxgE9TMBKVXGQjSgWACh2wBXAGx+e592CRPkE9sMcTXbsuYACYBTAGYBLMEoXN5y9ZoXCk+Xao1bJp-Vpkc2AZQrwARiB7466GI5duPR0R9XdxpJIL8aWyA

💻 Code

const cmp = <T,>(x: T, y: T) => x < y

null < null
cmp(null, null)

undefined < undefined
cmp(undefined, undefined)

Symbol() < Symbol()
cmp(Symbol(), Symbol())

🙁 Actual behavior

Error messages:

1. "The value 'null' cannot be used here.(18050)"
2. "The value 'undefined' cannot be used here.(18050)"
3. "The '<' operator cannot be applied to type 'symbol'.(2469)"

The errors show up for both operands of the relational operator except symbols, which only error on LHS.

The arrow fn cmp doesn't trigger any errors, even at call sites

🙂 Expected behavior

cmp should trigger an error on definition, because even though both params are same-type, they can't always be compared (symbols throw at runtime)

Additional information about the issue

No response

[fatcerberus]

Technically both parameters aren't even guaranteed to be the same type, because T might be a union.

[RyanCavanaugh]

See #52807; this is a rather breaky change to make and we're evaluating what the right course of action is. There are a lot of unconstrained (or insufficiently constrained) type parameters out there

[Rudxain]

Should I close this issue (as dupe) and open one about the weird single-sidedness of symbols? Or should I keep it as-is?

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.