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Make ref.cast succeed on null #161

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Nov 19, 2020
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Make ref.cast succeed on null #161

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6 changes: 4 additions & 2 deletions proposals/gc/MVP.md
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Original file line number Diff line number Diff line change
Expand Up @@ -382,10 +382,12 @@ RTT-based casts can only be performed with respect to concrete types, and requir
- returns 1 if the first operand is not null and its runtime type is a sub-RTT of the RTT operand, 0 otherwise

* `ref.cast <typeidx>` casts a reference value down to a type given by a RTT representation
- `ref.cast $t : [(ref null ht) (rtt n? $t)] -> [(ref $t)]`
- `ref.cast $t : [(ref null1? ht) (rtt n? $t)] -> [(ref null2? $t)]`
- iff `ht <: data` or `ht <: func`
- and `(type $t) <: ht`
- traps if the first operand is null or its runtime type is not a sub-RTT of the RTT operand
- and `null1? = null2?`
- returns null if the first operand is null
- traps if the first operand is not null and its runtime type is not a sub-RTT of the RTT operand

* `br_on_cast <labelidx> <typeidx>` branches if a value can be cast down to a given reference type
- `br_on_cast $l $t : [(ref null ht) (rtt n? $t)] -> [(ref null ht)]`
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