Solidity Modifiers – Difference Between `view` and `constant`

The paragraph specifically mentions that only function types are by default internal, and contract functions are by default public, even though I agree the wording is a little bit confusing. It says nowhere that they are at the same time both public and internal.

I think that there is some confusion to what a function type is. The same way you specify the type for a 256 int variable with the keyword uint256, you can also specify the type of a variable that will hold a function. The only difference is that this type declaration is a little more complex since functions are more complex and it looks like this:

function (param types) {internal|external} [pure|constant|view|payable] [returns (return types)] varName;

You can then assign to the variable varName a function that has the same type that you defined. This is only possible inside another function.

As a very simple example:

contract Example{
    function(uint256) returns (uint256) varName;

    function simpleFunction(uint256 parameter) returns (uint256){
        return parameter;
    }

    function test(){
        varName = simpleFunction;
    }
}

Where varName is the variable of function type, while simpleFunction and test are normal contract functions

Just so you have a simple definition for all those access classifiers:

• public - all can access
• external - Cannot be accessed internally, only externally
• internal - only this contract and contracts deriving from it can access
• private - can be accessed only from this contract

As you can notice private is a subset of internal and external is a subset of public.

Functions can be invoked in two different ways:

1. Via a transaction, which is broadcast to the network and changes blockchain state.
2. Via a call, which is performed locally on a single Ethereum network and does not change any blockchain state.

It's actually up to the client to decide which to do, but if a function is marked view, the default behavior of most clients (e.g. Remix, web3.js, etc.) is to use a call. That basically means running the transaction but not recording any state changes.

So in the above case, if you call B(), it will in effect give you back the value counter + 1. (During execution, it will increment the counter, but that change will simply be discarded.)

That said, you could invoke B() via a transaction, in which case the counter would truly be incremented in a persistent way. In essence, view is a hint to clients that they should use a call rather than a transaction.