PHP Variable

[Yokiest]

Okay so here is what i'm trying to do I'm making a Form Validation class that works with my Form Generation
and I would like to have default error messages and the ability to have custom error messages so I have
an array that has all the default error messages however certain error messages have a variable that isn't
defined till the validation function is ran so is there a way to have the variable take the value of the defined variable by the function

Default Array:

class formValidation{
    public $rules;
    public $error_messages = array(
             "alpha" => "This field must contain letters only.",
             "numeric" => "This field must contain numbers only.",
             "alphaNumeric" => "This field must contain letters and numbers only.",
             "minLength" => "This field must contain at least $length characters.",
             "maxLength" => "This field can not contain no more than $length characters."
             );
    public $errors; 

as you can see minLength and maxLength need $length but $length isn't defined until it is validated like so:

private function minLength($field,$length){
        if(strlen($field) <= $length){
            $this->errors[$field][] = $this->error_messages["minLenght"];
        }
    }
    private function maxLength($field,$lenght){
        if(strlen($field) >= $lenght){
            $this->errors[$field][] = $this->error_messages["maxLenght"];
        }
    } 

[NogDog]

Rather than embed a variable in a string, you'll probably just want to embed some sort of place-holder, e.g. "This field must contain at least {length} characters". Then when you actually use it, you would pass in your $length variable as a replacement value, e.g.:

$errorMsg = str_replace('{length}', $length, $error_messages['max_length']);