Re: conversion ctors question

I am baffled by this behaviour.

I have a class A declared as follows:

class A
{
public:
       A();
    explicit A(const std::string& value);
    explicit A(const TimestampParam& value) ;
    explicit A(const long value) ;
    explicit A(const double value) ;
    explicit A(const bool value) ;
    A(const Object& value) ;

    A(const A);

        A& operator= (const A&);
    ~A();
}

I am using the class in statements like this:

std::vector<A> params ;

//field id
A field(100L) ; //requires 'L' specifier else ambigious ctor
params.push_back(field);

//field name
field = A(std::string("Homer")); //ok
params.push_back(field);

!!! PRETZEL LOGIC ALERT !!!

//field descr
field = A("likes donuts"); //calls A::A(const bool)
params.push_back(field);

Why is the compiler casting a std::string to bool? I took of the
explicit keyword so I could automatically convert between the supported
types and A, and still, std::string is being cast as bool - WHY ??? -
and how do I fix this?