Pass parameters by reference and use iterators wherever possible

[ramsayleung]

Description

Currently the parameters mostly are passed by value, which means the compiler will Copy the parameter when passes them into a method, it's a little inefficient, then pass them by reference instead.

Using iterators wherever possible, since it's more atomic and rusty.

Fixed #127

Motivation and Context

Improve the efficiency of this library.

Dependencies

List any dependencies that are required for this change.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• All existing tests pass.
• Add some tests for iterator