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spec for view types (#15424)

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* spec for view types
* spec additions
* refactoring; there are two different kinds of views
* refactorings and spec additions
* enforce that view types are initialized
* enforce borrowing from the first formal parameter
* enforce lifetimes for borrowing of locals
* typo in the manual
* clarify in the implementation what a borrow operation really is
This commit is contained in:
Andreas Rumpf 2020-09-29 23:42:38 +02:00 • committed by GitHub
commit 4058801607
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11 changed files with 446 additions and 66 deletions
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13
tests/views/tcannot_borrow.nim
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@ -1,17 +1,22 @@
discard """
errormsg: "cannot borrow"
nimout: '''tcannot_borrow.nim(16, 7) Error: cannot borrow meh; what it borrows from is potentially mutated
tcannot_borrow.nim(17, 3) the mutation is here
tcannot_borrow.nim(16, 7) is the statement that connected the mutation to the parameter'''
line: 16
nimout: '''tcannot_borrow.nim(21, 7) Error: cannot borrow meh; what it borrows from is potentially mutated
tcannot_borrow.nim(22, 3) the mutation is here'''
line: 21
"""
{.experimental: "views".}
type
Foo = object
field: string
proc valid(s: var seq[Foo]) =
let v: lent Foo = s[0] # begin of borrow
echo v.field # end of borrow
s.setLen 0 # valid because 'v' isn't used afterwards
proc dangerous(s: var seq[Foo]) =
let meh: lent Foo = s[0]
s.setLen 0