How to withdraw PART of the Smart Contract's balance into an account?

Question

I have looked through many similar questions but they only address transferring the entirety of the smart contract's balance to the personal account, and it is done like this:

msg.sender.transfer(address(this).balance);

What I am trying (and failing) to figure out is how to transfer part of the balance. Eg. If the contract contains 3 ether, I only want to transfer 1. And I want to be able to specify the amount to be transferred every time I use the function. I am not posting my code because nothing I have tried works and it is pretty much guesswork.

Thank you for any help.

Answer 1

As Iftivar Taz mentioned if you are practicing to try msg.sender.transfer(amount). Try it with amount of 0 and it will probably work. Obviously your practicing contract won't have more than zero eths.

Answer 2

One way, expecting many searches

use List::MoreUtils qw(last_value);

my @entries = sort { $a <=> $b } keys %$calendarEntries;

my $nearest_le = last_value { $day >= $_ } @entries;

This returns the last element that is less or equal, for any input, so the key of interest.

The drawback of using simply a hash is that one needs an extra data structure to build. Any library that offers this sort of lookup must do that as well, of course, but those then come with other goodies and may be considerably better performing (depending on how often this is done).

If this 'rounding' need be done a lot for a given hash then it makes sense to build a lookup table for days, associating each with its nearest key in the hash.^†‡

If @entries is sorted descending ($b <=> $a) then the core List::Util::first does it.

---

^† For example

my %nearest_le;

my @keys = sort { $a <=> $b } keys %$calendarEntries;

for my $day (1..366) { 
    for my $k (@keys) { 
        if ($k <= $day) { 
            $nearest_le{$day} = $k; 
        }
        else { last }
    }   
}; 

This enumerates days of the year, as specified in the question.

---

^‡ If this were needed for things other than the days (366 at most), where long lists may be expected, a better algorithmic behavior is afforded by binary searches on sorted lists (O(log n)).

The library used above, List::MoreUtils, also has lower_bound with O(log n)

Returns the index of the first element in LIST which does not compare less than val.

So this needs a few adjustments, for

use List::MoreUtils qw(lower_bound);

my @keys = sort { $a <=> $b } keys %$calendarEntries;

my $nearest_le = exists $calendarEntries->{$day} 
    ? $day 
    : $keys[ -1 + lower_bound { $_ <=> $day } @keys ];

Answer 3

A nice simple solution.

use List::Util qw( max );

max grep { $_ <= $dayOfTheYear } keys %$calendarEntries

Notes:

• Best to make sure $calendarEntries->{ $dayOfTheYear } doesn't exist first.
• You'll need to handle the case where there is no matching key.

It's faster than sorting unless you perform many searches. But even then, we're only dealing with at most 365 keys, so simplicity is key here.

Answer 4

The simplest solution is to simply look up the value for your date, and if it is not found, go down until you find a value. In this sample, I included a rudimentary error handling.

use strict;
use warnings;
use feature 'say';

my $calendarEntries = { '1' => 'Entry 1', '5' => 'Entry 2', '15' => 'Entry 3' };
my $find = shift // 7;       # for testing purposes
my $date = get_nearest_below($calendarEntries, $find);
if (defined $date) {
    say "Nearest date below to '$find' is '$date'";
} else {                     # error handling
    warn "Nearest date below not found for '$find'";
}

sub get_nearest_below {
    my ($href, $n) = @_;
    while ($n > 0) {     # valid dates are > 0
        return $n if defined $href->{$n};   # find a defined value
        $n--;            # or go to the next key below
    }
    return undef;        # or return error if nothing is found before 0
}

Output:

$ foo.pl
Nearest date below to '7' is '5'

$ foo.pl 12
Nearest date below to '12' is '5'

$ foo.pl 123
Nearest date below to '123' is '15'

$ foo.pl 0
Nearest date below not found for '0' at foo.pl line 13.