github.com/gnolang/gno@v0.0.0-20240520182011-228e9d0192ce/tm2/pkg/store/firstlast.go (about)

     1  package store
     2  
     3  import (
     4  	"bytes"
     5  
     6  	"github.com/gnolang/gno/tm2/pkg/std"
     7  	"github.com/gnolang/gno/tm2/pkg/store/types"
     8  )
     9  
    10  // Gets the first item.
    11  func First(st Store, start, end []byte) (kv std.KVPair, ok bool) {
    12  	iter := st.Iterator(start, end)
    13  	if !iter.Valid() {
    14  		return kv, false
    15  	}
    16  	defer iter.Close()
    17  
    18  	return std.KVPair{Key: iter.Key(), Value: iter.Value()}, true
    19  }
    20  
    21  // Gets the last item.  `end` is exclusive.
    22  func Last(st Store, start, end []byte) (kv std.KVPair, ok bool) {
    23  	iter := st.ReverseIterator(end, start)
    24  	if !iter.Valid() {
    25  		if v := st.Get(start); v != nil {
    26  			return std.KVPair{Key: types.Cp(start), Value: types.Cp(v)}, true
    27  		}
    28  		return kv, false
    29  	}
    30  	defer iter.Close()
    31  
    32  	if bytes.Equal(iter.Key(), end) {
    33  		// Skip this one, end is exclusive.
    34  		iter.Next()
    35  		if !iter.Valid() {
    36  			return kv, false
    37  		}
    38  	}
    39  
    40  	return std.KVPair{Key: iter.Key(), Value: iter.Value()}, true
    41  }