private static Map<String, ExpressionFunction> toMap(Collection<ExpressionFunction> list) {
        Map<String,ExpressionFunction> mapBuilder = new HashMap<>();
        for (ExpressionFunction function : list)
            mapBuilder.put(function.getName(), function);
        return Map.copyOf(mapBuilder);
    }
Returns the type context of this, if it is able to resolve types.
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/rule/SerializationContext.java