proposal: Go 2: String interpolation

[xbt573]

Author background

• Would you consider yourself a novice, intermediate, or experienced Go programmer?
  Something between novice and intermediate
• What other languages do you have experience with?
  C#, Python, JS/TS

Related proposals

• Has this idea, or one like it, been proposed before?
  proposal: Go 2: string interpolation evaluating to string and list of expressions #50554
  proposal: Go 2: string interpolation #34174
  • If so, how does this proposal differ?
    This proposal defines different syntax
• Does this affect error handling?
  No
• Is this about generics?
  No

Proposal

• What is the proposed change?
  This proposal adds way to interpolate values to string other than fmt.Printf, concatenation, or others
• Who does this proposal help, and why?
  This proposal helps to make interpolation simple and don't remember all %something in fmt.Printf
• Please describe as precisely as possible the change to the language.
  This interpolation use strings, prefixed by hash (#) symbol, they converted to normal strings at runtime, because expressions can vary
• What would change in the language spec?
  Specification will include information about syntax of this string interpolation
• Is this change backward compatible?
  Yes
• Show example code before and after the change.
• Before

a := 5
hash := "#"

// Simple output
fmt.Printf("%v\n", a)

// Pad char
fmt.Printf("%-3v\n", hash)

• After

a := 5
hash := "#"

// You can even not import fmt!
// Simple output
println(#"{a}")

// Pad char (shows optional formatting)
println(#"{[%-3v] hash}")

• Orthogonality: how does this change interact or overlap with existing features?
  This is new feature
• Is the goal of this change a performance improvement?
  No

Costs

• Would this change make Go easier or harder to learn, and why?
  It's makes interpolation in Go easier to learn because of simple syntax
• What is the cost of this proposal? (Every language change has a cost).
  Implementation of this interpolation
• How many tools (such as vet, gopls, gofmt, goimports, etc.) would be affected?
  gopls, vet
• What is the compile time cost?
  Zero
• What is the run time cost?
  Additional interpolation
• Can you describe a possible implementation?
  No
• Do you have a prototype? (This is not required.)
  No

[ianlancetaylor]

Thanks. Closing as dup of #34174 and #50554.