libexpr: pass Exprs as references, not pointers

almost all places where Exprs are passed as pointers expect the pointers
to be non-null. pass them as references to encode this constraint in the
type system as well (and also communicate that Exprs must not be freed).

Change-Id: Ia98f166fec3c23151f906e13acb4a0954a5980a2

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 31d4ac9ff..4cce33eb1 100644
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -234,7 +234,7 @@ static void main_nix_build(int argc, char * * argv)
     DrvInfos drvs;
 
     /* Parse the expressions. */
-    std::vector<Expr *> exprs;
+    std::vector<std::reference_wrapper<Expr>> exprs;
 
     if (readStdin)
         exprs = {state->parseStdin()};
@@ -337,7 +337,7 @@ static void main_nix_build(int argc, char * * argv)
         if (!shell) {
 
             try {
-                auto expr = state->parseExprFromString(
+                auto & expr = state->parseExprFromString(
                     "(import <nixpkgs> {}).bashInteractive",
                     state->rootPath(CanonPath::fromCwd()));