hasAttr

lib.attrsets.hasAttr

Primop

Docs pulled from | This Revision | 16 minutes ago

Nix manual

Takes 2 arguments

s, set

hasAttr returns true if set has an attribute named s, and false if it does not. This is a dynamic version of the ? operator, since s is an expression rather than an identifier.

Unlike the ? operator, however, s cannot refer to a nested attribute set. Also unlike the ? operator, if s is not a string or set is not an attribute set, evaluation is aborted.

Has O(log n) time complexity, where n is number of attributes in the set.

Noogle detected

Aliases

Detected Type

hasAttr :: String -> AttrSet -> Bool

Implementation

This function is implemented in c++ and is part of the native nix runtime.

src/libexpr/primops.cc:3291

static void prim_hasAttr(EvalState & state, CallSite callSite, Value * const * args, Value & v)
{
    auto attr =
        state.forceStringNoCtx(*args[0], noPos, "while evaluating the first argument passed to builtins.hasAttr");
    state.forceAttrs(*args[1], noPos, "while evaluating the second argument passed to builtins.hasAttr");
    v.mkBool(args[1]->attrs()->get(state.symbols.create(attr)));
}

Implementation

The following is the current implementation of this function.

hasAttr