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authorShea Levy <shea@shealevy.com>2014-11-30T18·16-0500
committerShea Levy <shea@shealevy.com>2014-12-02T15·27-0500
commit320659b0cd161249c95e736c3fb309b1a73ea728 (patch)
treef58c49ae4828572d4642a4d02360f8a415a9f0f9 /src/libexpr/value-to-json.cc
parent5f04da905fcd01ea2d68cdbf7af41c836df5bb4e (diff)
Allow external code using libnixexpr to add types
Code that links to libnixexpr (e.g. plugins loaded with importNative, or
nix-exec) may want to provide custom value types and operations on
values of those types. For example, nix-exec is currently using sets
where a custom IO value type would be more appropriate. This commit
provides a generic hook for such types in the form of tExternal and the
ExternalBase virtual class, which contains all functions necessary for
libnixexpr's type-polymorphic functions (e.g. `showType`) to be
implemented.
Diffstat (limited to 'src/libexpr/value-to-json.cc')
-rw-r--r--src/libexpr/value-to-json.cc11
1 files changed, 11 insertions, 0 deletions
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
index d1ec9b566d66..b9f3e6551de1 100644
--- a/src/libexpr/value-to-json.cc
+++ b/src/libexpr/value-to-json.cc
@@ -80,10 +80,21 @@ void printValueAsJSON(EvalState & state, bool strict,
             break;
         }
 
+	case tExternal:
+            v.external->printValueAsJSON(state, strict, str, context);
+            break;
+
         default:
             throw TypeError(format("cannot convert %1% to JSON") % showType(v));
     }
 }
 
 
+void ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
+      std::ostream & str, PathSet & context)
+{
+    throw TypeError(format("cannot convert %1% to JSON") % showType());
+}
+
+
 }