Struct Literals

[cjllanwarne]

Especially when working with structs, needing to type in object at struct-construction time is slightly counter-intuitive.

As I was writing some of these out in test cases, I was thinking about more intuitive struct literals. Here are a few options:

• They all use A as the constructor indicator instead of object.
• 1 and 2 use {}, 3 and 4 ()
• 1 and 3 use variable names (eg i: ..., f:...), 2 and 4 do not.

struct A {
  Int i
  Float f
}
workflow foo {
  # Today's syntax:
  A a = object { i: 5, f: 5.5 }

  # Proposal 1:
  A a = A { i: 5, f: 5.5 }
  # Proposal 2:
  A a = A { 5, 5.5 }

  # Proposal 3:
  A a = A(i: 5, f: 5.5)
  # Proposal 4:
  A a = A(5, 5.5)
}

Any other thoughts?

---

Side note: why do we need anything at all before the { at all? Because otherwise the expression evaluates as a map literal and the key is actually an expression eg:

String i = "i"
String f = "g"

# oops, the 'f' key is actually "g", but we can't tell that until runtime:
A a = { i: 5, f: 5.5 }

NB: I think this side-note could lead to unexpected errors for authors. In the winstanley IDE I intend to flag the above pattern (ie a Struct value being assigned from a map literal) as a warning with the suggestion being "use an object/struct literal instead".

[orodeh]

@cjllanwarne I am for 1 or 2.

[orodeh]

Having chewed on it some more, I think braces (,) would be similar to object construction in standard programming languages. So, proposals 3 or 4. Another possibility:

# Proposal 1+2+3+4
A a = A( {i: 4, f: 5.5} )

We might want to allow all (or some) of these syntaxes. One way or the other, I suggest sticking to a known constructor syntax.

[patmagee]

Good suggestions @cjllanwarne. I like proposal 3 and proposal 1. leading with the property you are setting is clearer to me in this case and allows some flexibility in terms of order when creating a struct. Additionally, I think these work better for complex type, since it becomes clearer what property is being set. Whereas leaving out the property it looks a bit muddled imo.

struct A {
  Array[Pair[String,File]] complex
  Int i
}

workflow foo {
  #Proposal 1
  A a = A { complex: [{left:"string",right: "gs://abc"}, {left:"string", right:"gs://cba"}], i: 1231 }
  #Proposal 3
  A a = A ( complex: [{left:"string",right: "gs://abc"}, {left:"string", right:"gs://cba"}], i: 1231 )

  #Proposal 2 (Dont like this as much)
  A a = A {  [{left:"string",right: "gs://abc"}, {left:"string", right:"gs://cba"}], 1231 }
  #Proposal 4 (Dont like this either)
  A a = A ([{left:"string",right: "gs://abc"}, {left:"string", right:"gs://cba"}], 1231 )
}

[patmagee]

@cjllanwarne not sure if you have had time to look at this, but WDYT?

[patmagee]

implemented by #297