I need to create an index using a std:vector as the sort key. boost::lamda and std::sort seem just the thing: // Data vectors // // Goal is to sort index based on values of random // std::vector<int> index(10); // 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 std::vector<int> random(10); // random values, not in order namespace bll = boost::lambda ; // Sorted through vector pointer // // This compiles // std::vector<int> * ranp = & random; std::sort(index.begin(), index.end(), bll::var(*ranp)[bll::_1] < bll::var(*ranp)[bll::_2] ); In reality, my std::vector is wrapped in another object (for reasons given below, but unrelated to this question), with an operator[] to retrieve contents: // Container wrapper class Container { std::vector<int> _v; public: Container(std::vector<int> v) : _v(v) { } ; const int operator[](const int i) { return _v[i]; } }; // Sorted through container object // // This *does not* compile // Container * cvp = new Container(random); std::sort(index.begin(), index.end(), bll::var(*cvp)[bll::_1] < bll::var(*cvp)[bll::_2] ); /* Compiler error (g++ 4.01 (Apple)): obj-indexer.cc:95: instantiated from here boost/lambda/detail/operator_lambda_func_base.hpp:137: error: conversion from 'const int' to non-scalar type 'boost::lambda::detail::unspecified' requested */ I don't understand the error message, and can't make out from the documentation why this doesn't work. Do I need to extend the return type deduction system somehow? But operator[] is not one of the action types. Thanks for your help, Peter Aside: Why do I wrap std::vector inside Container? I'm memory constrained, so I combine a std::vector with a std::map to catch the overflows. The operator[i] then computes int ret = vector[i] + ( (o = map.find(i)) != map.end() ? o->second * 2^16 : 0); ____________ Peter Barnes pdbj@me.com ____________ Peter Barnes pdbj@me.com