Occasionally you want a complex format strings. Not bigger enough or enough of them to use a full blown template system. Rather than

var fields = new { name = "Bob", zipCode = "AB1234", phone =   "01234 567890" };
var address = String.Format("{0} : {1}", fields.name, fields.zipCode);
var phone = String.Format("{0} : {1}", fields.name, fields.phone);

it would be nice to write

var fields = new { name = "Bob", zipCode = "AB1234", phone = "01234 567890" };
var address = String.Format("{name} : {zipCode}", fields);
var phone = String.Format("{name} : {phone}", fields);

StringFill tries to provide an extension method Fill for System.String and AppendFill for System.Text.StringBuilder to provide this:

var sb = new StringBuilder();
sb.AppendFill("Hello {name}", new {name = "World"});

or

string actual = StringFill.Fill("exec SomeProc({arg1}, {arg2});",
                                new { arg1 = "Test", arg2 = "Example" });

Questions

Can I use it with Dictionary<string, object>? Yes, if you pass in a dictionary, generic or otherwise, it will perform the look up based on the keys of the dictionary rather than the properties.