That's what I intended as part of 'if you need the precision.' You're absolutely right that even if the beginning and end are floats, you may want to do the intermediate calculations as a double.
Therefore it's often important to have fp constants with as much bits as possible. But there are exceptions again: unless you use them to initialize float arrays etc.
Regarding indexes for arrays, there are typical uses that should be recognized: if I write a[ 1 ] I'd like to be able to address the element 1. If I write a[ 0xffffffffffff ] it's also clear it's more than 32 bits.
Right. There's tons of reasonable choices here. Which is why Rust currently has no defaults, and is why you need to write 5i today.
This whole topic is very much still under discussion. While many want defaults, what they default to is still a question. And there's a sizable group that doesn't want any default at all.
There is little performance advantage to using a 32-bit float. Their precision is low enough that you can't do anything useful without risking the correctness of your program.
They are, like shorts, an artefact of the past. Unlike shorts, their limitations are not within the intuition of the average programmer, which leads to widespread abuse and bugs.
Floats (and shorts) have a significant performance advantage, when they're appropriate. For example, you can fit 2x as many floats into cache compare to a double and good cache behaviour is really important these days, it's one of the reasons languages like C/C++/Rust with good control over memory layout can be very fast. Also, you can operate on 2x as many floats with vectorised instructions; again, SIMD is important these days, especially for things like games (where the precision of a float is fine).
This is too brutal, you have to consider the application domain. For physics simulations I would agree with you. For signal processing or graphics applications float is usually perfectly fine (and even overkill for many DSP applications).
People mentioned the cache efficiency gain with floats, and that is already relevant to rust. If in the future maybe rust could be used for GPGPU, then the difference between float and double often becomes even more dramatic. You definitely want to keep float support for this.
