expoter questions

• How to explain TreeNode type restriction and self-type in Spark's TreeNode?
• what if C++ class contains both const reference and non-const reference copy constructor?
• Is there any difference between C c; and C c = C();?
• What does the capital letter 'J' mean in cost function J(θ)?
• Why does the implementation of declval in libstdc++-v3 look so complicated?

expoter answers