Ruby: if – else – elsif – not – unless – true – false

if – else Statements

# statement-1
if item_counts[item_id] == nil
  item_counts[item_id] = 1
else
  item_counts[item_id] += 1
end

Another way of achieving the same outcome as statement-1 above:

# statement-2
if item_counts[item_id] == nil
  item_counts[item_id] = 0
end
item_counts[item_id] += 1

Another way of writing statement-2 above:

# statement-3
item_counts[item_id] = 0 if item_counts[item_id] == nil
item_counts[item_id] += 1

Another way of achieving the same outcome as statement-3 above:

# statement-4
item_counts[item_id] = 0 if !item_counts[item_id]
item_counts[item_id] += 1

Another way of achieving the same outcome as statement-4 above:

# statement-5
item_counts[item_id] = 0 unless item_counts[item_id]
item_counts[item_id] += 1

if – elsif – else Statements

# statement-6
if item_counts[item_id] == 1
  count = 1
elsif item_counts[item_id] == 2
  count = 2
else
  count = 0
end

Note that it is elsif, not elseif and not else if

True or False

In Ruby, every argument in a conditional expression is considered true except false and nil

pry> "Blue" if true
=> "Blue"

pry> "Blue" if 0
=> "Blue"

pry> "Blue" if false
=> nil

pry> "Blue" if nil
=> nil

pry> "Blue" if !nil
=> "Blue"