gistfile1.txt

typedef struct chan_t
{
    pthread_mutex_t  m_mu;
    pthread_cond_t   m_cond;
    int              closed;

    void (* dispose)(struct chan_t * self);
    ...
} chan_t;

typedef struct unbuffered_t
{
    chan_t base;
    ...
} unbuffered_t;

typedef struct buffered_t
{
    chan_t base;
    ...
} buffered_t;

chan_t* chan_init(int capacity)
{
    if (capacity)
    {
        buffered_t * ch = malloc(sizeof *ch);
        ch->dispose = dispose_buffered;
        ...
        return &ch->base;
    }
    else
    {
        Unbuffered_t * ch = malloc(sizeof *ch);
        ch->dispose = dispose_unbuffered;
        ...
        return &ch->base;
    }
}

void dispose_unbuffered(chan_t * self)
{
    unbuffered_t * ch = (chan_t*)self;
    ...
}

void dispose_buffered(chan_t * self)
{
    buffered_t * ch = (chan_t*)self;
    ...
}